Downlink channel reception method and user equipment, and downlink channel transmission method and base station

ABSTRACT

According to the present invention, a downlink control channel can be transmitted in varied numbers of OFDM symbols. The downlink control channel can be transmitted in a first number of OFDM symbols or can be transmitted in a second number of OFDM symbols. A user equipment can monitor a first downlink control channel candidate that spans the first number of OFDM symbols and can monitor a second downlink control channel candidate that spans the second number of OFDM symbols in a transmission time interval (TTI) for the reception of the downlink control channel. The downlink control channel can be transmitted by means of one or more control channel elements (CCE), each CCE comprising resources in the same OFDM symbol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2016/014459, filed on Dec. 9, 2016,which claims the benefit of U.S. Provisional Application No. 62/266,001,filed on Dec. 11, 2015, and 62/278,431, filed on Jan. 13, 2016, thecontents of which are all hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting/receivinga downlink channel.

BACKGROUND ART

With appearance and spread of machine-to-machine (M2M) communication anda variety of devices such as smartphones and tablet PCs and technologydemanding a large amount of data transmission, data throughput needed ina cellular network has rapidly increased. To satisfy such rapidlyincreasing data throughput, carrier aggregation technology, cognitiveradio technology, etc. for efficiently employing more frequency bandsand multiple input multiple output (MIMO) technology, multi-base station(BS) cooperation technology, etc. for raising data capacity transmittedon limited frequency resources have been developed.

A general wireless communication system performs datatransmission/reception through one downlink (DL) band and through oneuplink (UL) band corresponding to the DL band (in case of a frequencydivision duplex (FDD) mode), or divides a prescribed radio frame into aUL time unit and a DL time unit in the time domain and then performsdata transmission/reception through the UL/DL time unit (in case of atime division duplex (TDD) mode). A base station (BS) and a userequipment (UE) transmit and receive data and/or control informationscheduled on a prescribed time unit basis, e.g. on a subframe basis. Thedata is transmitted and received through a data region configured in aUL/DL subframe and the control information is transmitted and receivedthrough a control region configured in the UL/DL subframe. To this end,various physical channels carrying radio signals are formed in the UL/DLsubframe. In contrast, carrier aggregation technology serves to use awider UL/DL bandwidth by aggregating a plurality of UL/DL frequencyblocks in order to use a broader frequency band so that more signalsrelative to signals when a single carrier is used can be simultaneouslyprocessed.

In addition, a communication environment has evolved into increasingdensity of nodes accessible by a user at the periphery of the nodes. Anode refers to a fixed point capable of transmitting/receiving a radiosignal to/from the UE through one or more antennas. A communicationsystem including high-density nodes may provide a better communicationservice to the UE through cooperation between the nodes.

DISCLOSURE Technical Problem

Due to introduction of new radio communication technology, the number ofuser equipments (UEs) to which a BS should provide a service in aprescribed resource region increases and the amount of data and controlinformation that the BS should transmit to the UEs increases. Since theamount of resources available to the BS for communication with the UE(s)is limited, a new method in which the BS efficiently receives/transmitsuplink/downlink data and/or uplink/downlink control information usingthe limited radio resources is needed.

With development of technologies, overcoming delay or latency has becomean important challenge. Applications whose performance criticallydepends on delay/latency are increasing. Accordingly, a method to reducedelay/latency compared to the legacy system is demanded.

Also, with development of smart devices, a new scheme for efficientlytransmitting/receiving a small amount of data or efficientlytransmitting/receiving data occurring at a low frequency is required.

In addition, a signal transmission/reception method is required in thesystem supporting new radio access technologies.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solution

According to the present invention, a downlink control channel can betransmitted in a random number of OFDM symbols. The downlink controlchannel may be transmitted in a first number of OFDM symbols or a secondnumber of OFDM symbols. To receive the downlink control channel, a userequipment can monitor a first downlink control channel candidate thatspans the first number of OFDM symbols within a transmission timeinterval (TTI) and monitor a second downlink control channel candidatethat spans the second number of OFDM symbols within the TTI. Thedownlink control channel may be transmitted using one or more controlchannel elements (CCEs), each of which is configured with resources inthe same OFDM symbol.

In an aspect of the present invention, provided is a method forreceiving a downlink channel by a user equipment (UE) in a wirelesscommunication system, including: receiving a downlink control channelcarrying downlink control information within a transmission timeinterval (TTI); and receiving a downlink data channel based on thedownlink control information within the TTI. Receiving of the downlinkcontrol channel may include monitoring a first downlink control channelcandidate spanning T1 OFDM symbols within the TTI and monitoring asecond downlink control channel candidate spanning T2 OFDM symbolswithin the TTI. The downlink control channel may be the first downlinkcontrol channel candidate or the second downlink control channelcandidate. T1 may be different from T2. The downlink control channel maybe received using one or more control channel element (CCEs), and eachof the one or more CCEs may be configured with resources in the sameOFDM symbol.

In another aspect of the present invention, provided is a method fortransmitting a downlink channel by a base station (BS) in a wirelesscommunication system, including: transmitting a downlink control channelcarrying downlink control information within a transmission timeinterval (TTI); and transmitting a downlink data channel based on thedownlink control information within the TTI. The downlink controlchannel may be transmitted on either a first downlink control channelcandidate spanning T1 OFDM symbols within the TTI or a second downlinkcontrol channel candidate spanning T2 OFDM symbols within the TTI, andT1 may be different from T2. The downlink control channel may betransmitted using one or more control channel element (CCEs), and eachof the one or more CCEs may be configured with resources in the sameOFDM symbol.

In a further aspect of the present invention, provided is a userequipment (UE) for receiving a downlink channel in a wirelesscommunication system, including: a radio frequency (RF) unit; and aprocessor configured to control the RF unit. The processor may beconfigured to: control the RF unit to receive a downlink control channelcarrying downlink control information within a transmission timeinterval (TTI); and control the RF unit to receive a downlink datachannel based on the downlink control information within the TTI. Inaddition, wherein the processor may be configured to monitor a firstdownlink control channel candidate spanning T1 OFDM symbols within theTTI and monitor a second downlink control channel candidate spanning T2OFDM symbols within the TTI in order to receive the downlink controlchannel. The downlink control channel may be the first downlink controlchannel candidate or the second downlink control channel candidate. T1may be different from T2. The downlink control channel may be receivedusing one or more control channel element (CCEs), and each of the one ormore CCEs may be configured with resources in the same OFDM symbol.

In still another aspect of the present invention, provided is a basestation (BS) for transmitting a downlink channel in a wirelesscommunication system, including: a radio frequency (RF) unit; and aprocessor configured to control the RF unit. The processor may beconfigured to: control the RF unit to transmit a downlink controlchannel carrying downlink control information within a transmission timeinterval (TTI); and control the RF unit to transmit a downlink datachannel based on the downlink control information within the TTI. Thedownlink control channel may be transmitted on either a first downlinkcontrol channel candidate spanning T1 OFDM symbols within the TTI or asecond downlink control channel candidate spanning T2 OFDM symbolswithin the TTI, and T1 may be different from T2. The downlink controlchannel may be transmitted using one or more control channel element(CCEs), and each of the one or more CCEs may be configured withresources in the same OFDM symbol.

In each aspect of the present invention, the TTI may be equal to orsmaller than 0.5 ms in a time domain.

In each aspect of the present invention, the TTI may be configuredwithin a different TTI with a length of 1 ms in a time domain.

In each aspect of the present invention, the first downlink controlchannel candidate may occupy L1 CCEs, the second downlink controlchannel candidate may occupy L2 CCEs, and L2=(T1/T2)*L1, where L1 and L2are positive integers.

The above technical solutions are merely some parts of the embodimentsof the present invention and various embodiments into which thetechnical features of the present invention are incorporated can bederived and understood by persons skilled in the art from the followingdetailed description of the present invention.

Advantageous Effects

According to the present invention, uplink/downlink signals can beefficiently transmitted/received. Therefore, overall throughput of aradio communication system can be improved.

According to an embodiment of the present invention, delay/latencyoccurring during communication between a user equipment and a basestation may be reduced.

In addition, owing to development of smart devices, it is possible toefficiently transmit/receive not only a small amount of data but alsodata which occurs infrequently.

Moreover, signals can be transmitted/received in the system supportingnew radio access technologies.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

FIG. 2 illustrates the structure of a downlink (DL)/uplink (UL) slot ina wireless communication system.

FIG. 3 illustrates the structure of a DL subframe used in a wirelesscommunication system.

FIG. 4 illustrates the structure of a UL subframe used in a wirelesscommunication system.

FIG. 5 illustrates configuration of cell specific reference signals(CRSs) and user specific reference signals (UE-RS).

FIG. 6 is an example of a downlink control channel configured in a dataregion of a DL subframe.

FIG. 7 illustrates the length of a transmission time interval (TTI)which is needed to implement low latency.

FIG. 8 illustrates an example of a shortened TTI and an example oftransmission of a control channel and a data channel in a shortened TTI.

FIG. 9 illustrates an example of short TTIs configured in a legacysubframe.

FIG. 10 illustrates a self-contained subframe structure.

FIG. 11 illustrates an sPDCCH and transmission of a corresponding sPDSCHin a subframe where a legacy PDCCH is present.

FIG. 12 illustrates an sPDCCH search space according to the presentinvention.

FIG. 13 illustrates sPDCCH candidates according to the presentinvention.

FIG. 14 illustrates a time resource(s) of sPDCCH candidates according tothe present invention.

FIG. 15 illustrates an ECCE resource mapping method according to thepresent invention.

FIG. 16 illustrates another ECCE resource mapping method according tothe present invention.

FIG. 17 illustrates still another ECCE resource mapping method accordingto the present invention.

FIG. 18 illustrates a further ECCE resource mapping method according tothe present invention.

FIG. 19 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention. Thefollowing detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details.

In some instances, known structures and devices are omitted or are shownin block diagram form, focusing on important features of the structuresand devices, so as not to obscure the concept of the present invention.The same reference numbers will be used throughout this specification torefer to the same or like parts.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, it is assumed thatthe present invention is applied to 3GPP LTE/LTE-A. However, thetechnical features of the present invention are not limited thereto. Forexample, although the following detailed description is given based on amobile communication system corresponding to a 3GPP LTE/LTE-A system,aspects of the present invention that are not specific to 3GPP LTE/LTE-Aare applicable to other mobile communication systems.

For example, the present invention is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP LTE/LTE-A system in which an eNB allocatesa DL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the eNB.In a non-contention based communication scheme, an access point (AP) ora control node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmission device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmission devices always sense carrier of a networkand, if the network is empty, the transmission devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmission devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmission device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmissiondevice using a specific rule.

In the present invention, a user equipment (UE) may be a fixed or mobiledevice. Examples of the UE include various devices that transmit andreceive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present invention, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. In describing thepresent invention, a BS will be referred to as an eNB.

In the present invention, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of eNBs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be an eNB. For example, thenode may be a radio remote head (RRH) or a radio remote unit (RRU). TheRRH or RRU generally has a lower power level than a power level of aneNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connectedto the eNB through a dedicated line such as an optical cable,cooperative communication between RRH/RRU and the eNB can be smoothlyperformed in comparison with cooperative communication between eNBsconnected by a radio line. At least one antenna is installed per node.The antenna may mean a physical antenna or mean an antenna port or avirtual antenna.

In the present invention, a cell refers to a prescribed geographicalarea to which one or more nodes provide a communication service.Accordingly, in the present invention, communicating with a specificcell may mean communicating with an eNB or a node which provides acommunication service to the specific cell. In addition, a DL/UL signalof a specific cell refers to a DL/UL signal from/to an eNB or a nodewhich provides a communication service to the specific cell. A nodeproviding UL/DL communication services to a UE is called a serving nodeand a cell to which UL/DL communication services are provided by theserving node is especially called a serving cell. Furthermore, channelstatus/quality of a specific cell refers to channel status/quality of achannel or communication link formed between an eNB or node whichprovides a communication service to the specific cell and a UE. The UEmay measure DL channel state received from a specific node usingcell-specific reference signal(s) (CRS(s)) transmitted on a CRS resourceand/or channel state information reference signal(s) (CSI-RS(s))transmitted on a CSI-RS resource, allocated by antenna port(s) of thespecific node to the specific node. Detailed CSI-RS configuration may beunderstood with reference to 3GPP TS 36.211 and 3GPP TS 36.331documents.

Meanwhile, a 3GPP LTE/LTE-A system uses the concept of a cell in orderto manage radio resources and a cell associated with the radio resourcesis distinguished from a cell of a geographic region.

A “cell” of a geographic region may be understood as coverage withinwhich a node can provide service using a carrier and a “cell” of a radioresource is associated with bandwidth (BW) which is a frequency rangeconfigured by the carrier. Since DL coverage, which is a range withinwhich the node is capable of transmitting a valid signal, and ULcoverage, which is a range within which the node is capable of receivingthe valid signal from the UE, depends upon a carrier carrying thesignal, the coverage of the node may be associated with coverage of the“cell” of a radio resource used by the node. Accordingly, the term“cell” may be used to indicate service coverage of the node sometimes, aradio resource at other times, or a range that a signal using a radioresource can reach with valid strength at other times. The “cell” of theradio resource will be described later in more detail.

3GPP LTE/LTE-A standards define DL physical channels corresponding toresource elements carrying information derived from a higher layer andDL physical signals corresponding to resource elements which are used bya physical layer but which do not carry information derived from ahigher layer. For example, a physical downlink shared channel (PDSCH), aphysical broadcast channel (PBCH), a physical multicast channel (PMCH),a physical control format indicator channel (PCFICH), a physicaldownlink control channel (PDCCH), and a physical hybrid ARQ indicatorchannel (PHICH) are defined as the DL physical channels, and a referencesignal and a synchronization signal are defined as the DL physicalsignals. A reference signal (RS), also called a pilot, refers to aspecial waveform of a predefined signal known to both a BS and a UE. Forexample, a cell-specific RS (CRS), a UE-specific RS (UE-RS), apositioning RS (PRS), and channel state information RS (CSI-RS) may bedefined as DL RSs. Meanwhile, the 3GPP LTE/LTE-A standards define ULphysical channels corresponding to resource elements carryinginformation derived from a higher layer and UL physical signalscorresponding to resource elements which are used by a physical layerbut which do not carry information derived from a higher layer. Forexample, a physical uplink shared channel (PUSCH), a physical uplinkcontrol channel (PUCCH), and a physical random access channel (PRACH)are defined as the UL physical channels, and a demodulation referencesignal (DM RS) for a UL control/data signal and a sounding referencesignal (SRS) used for UL channel measurement are defined as the ULphysical signals.

In the present invention, a physical downlink control channel (PDCCH), aphysical control format indicator channel (PCFICH), a physical hybridautomatic retransmit request indicator channel (PHICH), and a physicaldownlink shared channel (PDSCH) refer to a set of time-frequencyresources or resource elements (REs) carrying downlink controlinformation (DCI), a set of time-frequency resources or REs carrying acontrol format indicator (CFI), a set of time-frequency resources or REscarrying downlink acknowledgement (ACK)/negative ACK (NACK), and a setof time-frequency resources or REs carrying downlink data, respectively.In addition, a physical uplink control channel (PUCCH), a physicaluplink shared channel (PUSCH) and a physical random access channel(PRACH) refer to a set of time-frequency resources or REs carryinguplink control information (UCI), a set of time-frequency resources orREs carrying uplink data and a set of time-frequency resources or REscarrying random access signals, respectively. In the present invention,in particular, a time-frequency resource or RE that is assigned to orbelongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to asPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE orPDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource,respectively. Therefore, in the present invention, PUCCH/PUSCH/PRACHtransmission of a UE is conceptually identical to UCI/uplink data/randomaccess signal transmission on PUSCH/PUCCH/PRACH, respectively. Inaddition, PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB isconceptually identical to downlink data/DCI transmission onPDCCH/PCFICH/PHICH/PDSCH, respectively.

Hereinafter, OFDM symbol/subcarrier/RE to or for whichCRS/DMRS/CSI-RS/SRS/UE-RS/TRS is assigned or configured will be referredto as CRS/DMRS/CSI-RS/SRS/UE-RS/TRS symbol/carrier/subcarrier/RE. Forexample, an OFDM symbol to or for which a tracking RS (TRS) is assignedor configured is referred to as a TRS symbol, a subcarrier to or forwhich the TRS is assigned or configured is referred to as a TRSsubcarrier, and an RE to or for which the TRS is assigned or configuredis referred to as a TRS RE. In addition, a subframe configured fortransmission of the TRS is referred to as a TRS subframe. Moreover, asubframe in which a broadcast signal is transmitted is referred to as abroadcast subframe or a PBCH subframe and a subframe in which asynchronization signal (e.g. PSS and/or SSS) is transmitted is referredto a synchronization signal subframe or a PSS/SSS subframe. OFDMsymbol/subcarrier/RE to or for which PSS/SSS is assigned or configuredis referred to as PSS/SSS symbol/subcarrier/RE, respectively.

In the present invention, a CRS port, a UE-RS port, a CSI-RS port, and aTRS port refer to an antenna port configured to transmit a CRS, anantenna port configured to transmit a UE-RS, an antenna port configuredto transmit a CSI-RS, and an antenna port configured to transmit a TRS,respectively. Antenna ports configured to transmit CRSs may bedistinguished from each other by the locations of REs occupied by theCRSs according to CRS ports, antenna ports configured to transmit UE-RSsmay be distinguished from each other by the locations of REs occupied bythe UE-RSs according to UE-RS ports, and antenna ports configured totransmit CSI-RSs may be distinguished from each other by the locationsof REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, theterm CRS/UE-RS/CSI-RS/TRS ports may also be used to indicate a patternof REs occupied by CRSs/UE-RSs/CSI-RSs/TRSs in a predetermined resourceregion. In the present invention, both a DMRS and a UE-RS refer to RSsfor demodulation and, therefore, the terms DMRS and UE-RS are used torefer to RSs for demodulation.

For terms and technologies which are not specifically described amongthe terms of and technologies employed in this specification, 3GPPLTE/LTE-A standard documents, for example, 3GPP TS 36.211, 3GPP TS36.212, 3GPP TS 36.213, 3GPP TS 36.321 and 3GPP TS 36.331 may bereferenced.

FIG. 1 illustrates the structure of a radio frame used in a wirelesscommunication system.

Specifically, FIG. 1(a) illustrates an exemplary structure of a radioframe which can be used in frequency division multiplexing (FDD) in 3GPPLTE/LTE-A and FIG. 1(b) illustrates an exemplary structure of a radioframe which can be used in time division multiplexing (TDD) in 3GPPLTE/LTE-A.

Referring to FIG. 1, a 3GPP LTE/LTE-A radio frame is 10 ms(307,200T_(s)) in duration. The radio frame is divided into 10 subframesof equal size. Subframe numbers may be assigned to the 10 subframeswithin one radio frame, respectively. Here, T_(s) denotes sampling timewhere T_(s)=1/(2048*15 kHz). Each subframe is 1 ms long and is furtherdivided into two slots. 20 slots are sequentially numbered from 0 to 19in one radio frame. Duration of each slot is 0.5 ms. A time interval inwhich one subframe is transmitted is defined as a transmission timeinterval (TTI). Time resources may be distinguished by a radio framenumber (or radio frame index), a subframe number (or subframe index), aslot number (or slot index), and the like.

A TTI refers to an interval at which data may be scheduled. For example,referring to FIGS. 1 and 3, the transmission opportunity of a UL grantor DL grant is given every 1 ms in the current LTE/LTE-A system. TheUL/DL grant opportunity is not given several times within a time shorterthan 1 ms. Accordingly, the TTI is 1 ms in the current LTE-LTE-A system.

A radio frame may have different configurations according to duplexmodes. In FDD mode for example, since DL transmission and ULtransmission are discriminated according to frequency, a radio frame fora specific frequency band operating on a carrier frequency includeseither DL subframes or UL subframes. In TDD mode, since DL transmissionand UL transmission are discriminated according to time, a radio framefor a specific frequency band operating on a carrier frequency includesboth DL subframes and UL subframes.

Table 1 shows an exemplary UL-DL configuration within a radio frame inTDD mode.

TABLE 1 Uplink- Downlink- downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D DD D D 6 5 ms D S U U U D S U U D

In Table 1, D denotes a DL subframe, U denotes a UL subframe, and Sdenotes a special subframe. The special subframe includes three fields,i.e. downlink pilot time slot (DwPTS), guard period (GP), and uplinkpilot time slot (UpPTS). DwPTS is a time slot reserved for DLtransmission and UpPTS is a time slot reserved for UL transmission.Table 2 shows an example of the special subframe configuration.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special subframe Normal cyclic Extended cyclicNormal cyclic Extended cyclic configuration DwPTS prefix in uplinkprefix in uplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — —9 13168 · T_(s) — — —

FIG. 2 illustrates the structure of a DL/UL slot structure in a wirelesscommunication system.

Referring to FIG. 2, a slot includes a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols in the time domain and includes aplurality of resource blocks (RBs) in the frequency domain. The OFDMsymbol may refer to one symbol duration. Referring to FIG. 2, a signaltransmitted in each slot may be expressed by a resource grid includingN^(DL/UL) _(RB)*N^(RB) _(sc) subcarriers and N^(DL/UL) _(symb) OFDMsymbols. N^(DL) _(RB) denotes the number of RBs in a DL slot and N^(UL)_(RB) denotes the number of RBs in a UL slot. N^(DL) _(RB) and N^(DL)_(RB) depend on a DL transmission bandwidth and a UL transmissionbandwidth, respectively. N^(DL) _(symb) denotes the number of OFDMsymbols in a DL slot, N^(UL) _(symb) denotes the number of OFDM symbolsin a UL slot, and N^(RB) _(sc) denotes the number of subcarriersconfiguring one RB.

An OFDM symbol may be referred to as an OFDM symbol, a single carrierfrequency division multiplexing (SC-FDM) symbol, etc. according tomultiple access schemes. The number of OFDM symbols included in one slotmay be varied according to channel bandwidths and CP lengths. Forexample, in a normal cyclic prefix (CP) case, one slot includes 7 OFDMsymbols. In an extended CP case, one slot includes 6 OFDM symbols.Although one slot of a subframe including 7 OFDM symbols is shown inFIG. 2 for convenience of description, embodiments of the presentinvention are similarly applicable to subframes having a differentnumber of OFDM symbols. Referring to FIG. 2, each OFDM symbol includesN^(DL/UL) _(RB)*/V^(RB) _(sc) subcarriers in the frequency domain. Thetype of the subcarrier may be divided into a data subcarrier for datatransmission, a reference signal (RS) subcarrier for RS transmission,and a null subcarrier for a guard band and a DC component. The nullsubcarrier for the DC component is unused and is mapped to a carrierfrequency f₀ in a process of generating an OFDM signal or in a frequencyup-conversion process. The carrier frequency is also called a centerfrequency f_(c).

One RB is defined as N^(DL/UL) _(symb) (e.g. 7) consecutive OFDM symbolsin the time domain and as N^(RB) _(sc) (e.g. 12) consecutive subcarriersin the frequency domain. For reference, a resource composed of one OFDMsymbol and one subcarrier is referred to a resource element (RE) ortone. Accordingly, one RB includes N^(DL/DL) _(symb)*N^(RB) _(sc) REs.Each RE within a resource grid may be uniquely defined by an index pair(k, l) within one slot. k is an index ranging from 0 to N^(DL/UL)_(RB)*N^(RB) _(sc)−1 in the frequency domain, and/is an index rangingfrom 0 to N^(DL/UL) _(symb)−1 in the time domain.

Meanwhile, one RB is mapped to one physical resource block (PRB) and onevirtual resource block (VRB). A PRB is defined as N^(DL) _(symb) (e.g.7) consecutive OFDM or SC-FDM symbols in the time domain and N^(RB)_(sc) (e.g. 12) consecutive subcarriers in the frequency domain.Accordingly, one PRB is configured with N^(DL/UL) _(symb)*N^(RB) _(sc)REs. In one subframe, two RBs each located in two slots of the subframewhile occupying the same N^(RB) _(sc) consecutive subcarriers arereferred to as a physical resource block (PRB) pair. Two RBs configuringa PRB pair have the same PRB number (or the same PRB index).

FIG. 3 illustrates the structure of a DL subframe used in a wirelesscommunication system.

Referring to FIG. 3, a DL subframe is divided into a control region anda data region in the time domain. Referring to FIG. 3, a maximum of 3(or 4) OFDM symbols located in a front part of a first slot of asubframe corresponds to the control region. Hereinafter, a resourceregion for PDCCH transmission in a DL subframe is referred to as a PDCCHregion. OFDM symbols other than the OFDM symbol(s) used in the controlregion correspond to the data region to which a physical downlink sharedchannel (PDSCH) is allocated. Hereinafter, a resource region availablefor PDSCH transmission in the DL subframe is referred to as a PDSCHregion.

Examples of a DL control channel used in 3GPP LTE include a physicalcontrol format indicator channel (PCFICH), a physical downlink controlchannel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc.

The PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols available fortransmission of a control channel within a subframe. The PCFICH notifiesthe UE of the number of OFDM symbols used for the corresponding subframeevery subframe. The PCFICH is located at the first OFDM symbol. ThePCFICH is configured by four resource element groups (REGs), each ofwhich is distributed within a control region on the basis of cell ID.One REG includes four REs.

A set of OFDM symbols available for the PDCCH at a subframe is given bythe following Table.

TABLE 3 Number of OFDM Number of symbols for OFDM PDCCH symbols for whenPDCCH when Subframe N^(DL) _(RB) > 10 N^(DL) _(RB) ≤ 10 Subframe 1 and 6for frame structure 1, 2 2 type 2 MBSFN subframes on a carrier 1, 2 2supporting PDSCH, configured with 1 or 2 cell-specfic antenna portsMBSFN subframes on a carrier 2 2 supporting PDSCH, configured with 4cell-specific antenna ports Subframes on a carrier not supporting 0 0PDSCH Non-MBSFN subframes (except subframe 1, 2, 3 2, 3 6 for framestructure type 2) configured with positioning reference signals Allother cases 1, 2, 3 2, 3, 4

A subset of downlink subframes within a radio frame on a carrier forsupporting PDSCH transmission may be configured as MBSFN subframe(s) bya higher layer. Each MBSFN subframe is divided into a non-MBSFN regionand an MBSFN region. The non-MBSFN region spans first one or two OFDMsymbols, and its length is given by Table 3. The same CP as cyclicprefix (CP) used for subframe 0 is used for transmission within thenon-MBSFN region of the MBSFN subframe. The MBSFN region within theMBSFN subframe is defined as OFDM symbols which are not used in thenon-MBSFN region.

The PCFICH carries a control format indicator (CFI), which indicates anyone of values of 1 to 3. For a downlink system bandwidth N^(DL)_(RB)>10, the number 1, 2 or 3 of OFDM symbols which are spans of DCIcarried by the PDCCH is given by the CFI. For a downlink systembandwidth N^(DL) _(RB)≤10, the number 2, 3 or 4 of OFDM symbols whichare spans of DCI carried by the PDCCH is given by CFI+1.

The PHICH carries a HARQ (Hybrid Automatic Repeat Request) ACK/NACK(acknowledgment/negative-acknowledgment) signal as a response to ULtransmission. The PHICH includes three REGs, and is scrambledcell-specifically. ACK/NACK is indicated by 1 bit, and the ACK/NACK of 1bit is repeated three times. Each of the repeated ACK/NACK bits isspread with a spreading factor (SF) 4 or 2 and then mapped into acontrol region.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The DCI includes resourceallocation information for a UE or UE group and other controlinformation. Transmit format and resource allocation information of adownlink shared channel (DL-SCH) are referred to as DL schedulinginformation or DL grant. Transmit format and resource allocationinformation of an uplink shared channel (UL-SCH) are referred to as ULscheduling information or UL grant. The size and usage of the DCIcarried by one PDCCH are varied depending on DCI formats. The size ofthe DCI may be varied depending on a coding rate. In the current 3GPPLTE system, various formats are defined, wherein formats 0 and 4 aredefined for a UL, and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, 3 and 3Aare defined for a DL. Combination selected from control information suchas a hopping flag, RB allocation, modulation coding scheme (MCS),redundancy version (RV), new data indicator (NDI), transmit powercontrol (TPC), cyclic shift, cyclic shift demodulation reference signal(DM RS), UL index, channel quality information (CQI) request, DLassignment index, HARQ process number, transmitted precoding matrixindicator (TPMI), precoding matrix indicator (PMI) information istransmitted to the UE as the DCI. The following table shows examples ofDCI formats.

TABLE 4 DCI format Description 0 Resource grants for the PUSCHtransmissions (uplink) 1 Resource assignments for single codeword PDSCHtransmissions 1A Compact signaling of resource assignments for singlecodeword PDSCH 1B Compact signaling of resource assignments for singlecodeword PDSCH 1C Very compact resource assignments for PDSCH (e.g.paging/broadcast system information) 1D Compact resource assignments forPDSCH using multi-user MIMO 2 Resource assignments for PDSCH forclosed-loop MIMO operation 2A Resource assignments for PDSCH foropen-loop MIMO operation 2B Resource assignments for PDSCH using up to 2antenna ports with UE-specific reference signals 2C Resource assignmentfor PDSCH using up to 8 antenna ports with UE-specific reference signals3/3A Power control commands for PUCCH and PUSCH with 2-bit/1-bit poweradjustments 4 Scheduling of PUSCH in one UL Component Carrier withmulti-antenna port transmission mode

Other DCI formats in addition to the DCI formats defined in Table 4 maybe defined.

A plurality of PDCCHs may be transmitted within a control region. A UEmay monitor the plurality of PDCCHs. An eNB determines a DCI formatdepending on the DCI to be transmitted to the UE, and attaches cyclicredundancy check (CRC) to the DCI. The CRC is masked (or scrambled) withan identifier (for example, a radio network temporary identifier (RNTI))depending on usage of the PDCCH or owner of the PDCCH. For example, ifthe PDCCH is for a specific UE, the CRC may be masked with an identifier(for example, cell-RNTI (C-RNTI)) of the corresponding UE. If the PDCCHis for a paging message, the CRC may be masked with a paging identifier(for example, paging-RNTI (P-RNTI)). If the PDCCH is for systeminformation (in more detail, system information block (SIB)), the CRCmay be masked with system information RNTI (SI-RNTI). If the PDCCH isfor a random access response, the CRC may be masked with a random accessRNTI (RA-RNTI). For example, CRC masking (or scrambling) includes XORoperation of CRC and RNTI at the bit level.

Generally, a DCI format, which may be transmitted to the UE, is varieddepending on a transmission mode configured for the UE. In other words,certain DCI format(s) corresponding to the specific transmission modenot all DCI formats may only be used for the UE configured to a specifictransmission mode.

For example, a transmission mode is semi-statically configured for theUE to allow the UE to receive a PDSCH which is transmitted according toone of a plurality of predefined transmission modes. The UE attempts todecode the PDCCH using only DCI formats corresponding to thetransmission mode thereof. In other words, in order to maintain thecomputational load of the UE according to an attempt of blind decodingat a level lower than or equal to a certain level, not all DCI formatsare simultaneously searched by the UE. Table 5 shows transmission modesfor configuring the MIMO technology and DCI formats used by the UE toperform blind decoding in the corresponding transmission modes. Inparticular, Table 6 shows a relationship between the PDCCH and PDSCHconfigured by a cell radio network temporary identifier (cell RNTI orC-RNTI).

TABLE 5 Transmission Transmission scheme of PDSCH mode DCI format SearchSpace corresponding to PDCCH Mode 1 DCI format 1A Common andSingle-antenna port, port 0 UE specific by C- RNTI DCI format 1 UEspecific by C- Single-antenna port, port 0 RNTI Mode 2 DCI format 1ACommon and Transmit diversity UE specific by C- RNTI DCI format 1 UEspecific by C- Transmit diversity RNTI Mode 3 DCI format 1A Common andTransmit diversity UE specific by C- RNTI DCI format 2A UE specific byC- Large delay CDD or Transmit diversity RNTI Mode 4 DCI format 1ACommon and Transmit diversity UE specific by C- RNTI DCI format 2 UEspecific by C- Closed-loop spatial multiplexing or RNTI Transmitdiversity Mode 5 DCI format 1A Common and Transmit diversity UE specificby C- RNTI DCI format 1D UE specific by C- Multi-user MIMO RNTI Mode 6DCI format 1A Common and Transmit diversity UE specific by C- RNTI DCIformat 1B UE specific by C- Closed-loop spatial multiplexing using RNTIa single transmission layer Mode 7 DCI format 1A Common and If thenumber of PBCH antenna ports UE specific by C- is one, Single-antennaport, port 0 is RNTI used, otherwise Transmit diversity DCI format 1 UEspecific by C- Single-antenna port, port 5 RNTI Mode 8 DCI format 1ACommon and If the number of PBCH antenna ports UE specific by C- is one,Single-antenna port, port 0 is RNTI used, otherwise Transmit diversityDCI format 2B UE specific by C- Dual layer transmission, port 7 and 8RNTI or single-antenna port, port 7 or 8 Mode 9 DCI format 1A Common andNon-MBSFN subframe: If the number UE specific by C- of PBCH antennaports is one, Single- RNTI antenna port, port 0 is used, otherwiseTransmit diversity. MBSFN subframe: Single-antenna port, port 7 DCIformat 2C UE specific by C- Up to 8 layer transmission, ports 7-14 RNTIor single-antenna port, port 7 or 8 Mode 10 DCI format 1A Common andNon-MBSFN subframe: If the number UE specific by C- of PBCH antennaports is one, Single- RNTI antenna port, port 0 is used, otherwiseTransmit diversity. MBSFN subframe: Single-antenna port, port 7 DCIformat 2D UE specific by C- Up to 8 layer transmission, ports 7-14 RNTIor single antenna port, port 7 or 8

Although transmission modes 1 to 10 are listed in Table 5, othertransmission modes in addition to the transmission modes defined inTable 5 may be defined.

Referring to Table 5, a UE configured to a transmission mode 9, forexample, tries to decode PDCCH candidates of a UE-specific search space(USS) to a DCI format 1A, and tries to decode PDCCH candidates of acommon search space (CSS) and the USS to a DCI format 2C. The UE maydecode a PDSCH in accordance with DCI based on the DCI formatsuccessfully decoded. If DCI decoding from one of a plurality of PDCCHcandidates to the DCI format 1A is successfully performed, the UE maydecode the PDSCH by assuming that up to 8 layers from antenna ports 7 to14 are transmitted thereto through the PDSCH, or may decode the PDSCH byassuming that a single layer from the antenna port 7 or 8 is transmittedthereto through the PDSCH.

The PDCCH is allocated to first m number of OFDM symbol(s) within asubframe, where m is an integer equal to or greater than 1, and isindicated by the PCFICH.

The PDCCH is transmitted on an aggregation of one or a plurality ofcontinuous control channel elements (CCEs). The CCE is a logicallocation unit used to provide a coding rate based on the status of aradio channel to the PDCCH. The CCE corresponds to a plurality ofresource element groups (REGs). For example, each CCE contains 9 REGs,which are distributed across the first 1/2/3 (/4 if needed for a 1.4 MHzchannel) OFDM symbols and the system bandwidth through interleaving toenable diversity and to mitigate interference. One REG corresponds tofour REs. Four QPSK symbols are mapped to each REG. A resource element(RE) occupied by the reference signal (RS) is not included in the REG.Accordingly, the number of REGs within given OFDM symbols is varieddepending on the presence of the RS. The REGs are also used for otherdownlink control channels (that is, PDFICH and PHICH).

Assuming that the number of REGs not allocated to the PCFICH or thePHICH is N_(REG), the number of available CCEs in a DL subframe forPDCCH(s) in a system is numbered from 0 to N_(CCE)−1, whereN_(CCE)=floor(N_(REG)/9).

A PDCCH format and the number of DCI bits are determined in accordancewith the number of CCEs. The CCEs are numbered and consecutively used.To simplify the decoding process, a PDCCH having a format including nCCEs may be initiated only on CCEs assigned numbers corresponding tomultiples of n. The number of CCEs used for transmission of a specificPDCCH is determined by a network or the eNB in accordance with channelstatus. For example, one CCE may be required for a PDCCH for a UE (forexample, adjacent to eNB) having a good downlink channel. However, incase of a PDCCH for a UE (for example, located near the cell edge)having a poor channel, eight CCEs may be required to obtain sufficientrobustness. Additionally, a power level of the PDCCH may be adjusted tocorrespond to a channel status.

In a 3GPP LTE/LTE-A system, a set of CCEs on which a PDCCH can belocated for each UE is defined. A CCE set in which the UE can detect aPDCCH thereof is referred to as a PDCCH search space or simply as asearch space (SS). An individual resource on which the PDCCH can betransmitted in the SS is called a PDCCH candidate. A set of PDCCHcandidates that the UE is to monitor is defined in terms of SSs, where asearch space S^((L)) _(k) at aggregation level L∈{1, 2, 4, 8} is definedby a set of PDCCH candidates. SSs for respective PDCCH formats may havedifferent sizes and a dedicated SS and a common SS are defined. Thededicated SS is a UE-specific SS (USS) and is configured for eachindividual UE. The common SS (CSS) is configured for a plurality of UEs.

The following Table shows an example of aggregation levels for definingSS.

TABLE 6 Number of Search space S^((L)) _(k) PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE- 1 6 6 specific 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

The eNB transmits an actual PDCCH (DCI) on a PDCCH candidate in a searchspace and the UE monitors the search space to detect the PDCCH (DCI).Here, monitoring implies attempting to decode each PDCCH in thecorresponding SS according to all monitored DCI formats. The UE maydetect a PDCCH thereof by monitoring a plurality of PDCCHs. Basically,the UE does not know the location at which a PDCCH thereof istransmitted. Therefore, the UE attempts to decode all PDCCHs of thecorresponding DCI format for each subframe until a PDCCH having an IDthereof is detected and this process is referred to as blind detection(or blind decoding (BD)).

For example, it is assumed that a specific PDCCH is CRC-masked with aradio network temporary identity (RNTI) ‘A’ and information about datatransmitted using a radio resource ‘B’ (e.g. frequency location) andusing transport format information ‘C’ (e.g. transmission block size,modulation scheme, coding information, etc.) is transmitted in aspecific DL subframe. Then, the UE monitors the PDCCH using RNTIinformation thereof. The UE having the RNTI ‘A’ receives the PDCCH andreceives the PDSCH indicated by ‘B’ and ‘C’ through information of thereceived PDCCH.

FIG. 4 illustrates the structure of a UL subframe used in a wirelesscommunication system.

Referring to FIG. 4, a UL subframe may be divided into a data region anda control region in the frequency domain. One or several PUCCHs may beallocated to the control region to deliver UCI. One or several PUSCHsmay be allocated to the data region of the UE subframe to carry userdata.

In the UL subframe, subcarriers distant from a direct current (DC)subcarrier are used as the control region. In other words, subcarrierslocated at both ends of a UL transmission BW are allocated to transmitUCI. A DC subcarrier is a component unused for signal transmission andis mapped to a carrier frequency f₀ in a frequency up-conversionprocess. A PUCCH for one UE is allocated to an RB pair belonging toresources operating on one carrier frequency and RBs belonging to the RBpair occupy different subcarriers in two slots. The PUCCH allocated inthis way is expressed by frequency hopping of the RB pair allocated tothe PUCCH over a slot boundary. If frequency hopping is not applied, theRB pair occupies the same subcarriers.

The PUCCH may be used to transmit the following control information.

-   -   Scheduling request (SR): SR is information used to request a        UL-SCH resource and is transmitted using an on-off keying (OOK)        scheme.    -   HARQ-ACK: HARQ-ACK is a response to a PDCCH and/or a response to        a DL data packet (e.g. a codeword) on a PDSCH. HARQ-ACK        indicates whether the PDCCH or PDSCH has been successfully        received. 1-bit HARQ-ACK is transmitted in response to a single        DL codeword and 2-bit HARQ-ACK is transmitted in response to two        DL codewords. A HARQ-ACK response includes a positive ACK        (simply, ACK), negative ACK (NACK), discontinuous transmission        (DTX), or NACK/DRX. HARQ-ACK is used interchangeably with HARQ        ACK/NACK and ACK/NACK.    -   Channel state information (CSI): CSI is feedback information for        a DL channel. CSI may include channel quality information (CQI),        a precoding matrix indicator (PMI), a precoding type indicator,        and/or a rank indicator (RI). In the CSI, MIMO-related feedback        information includes the RI and the PMI. The RI indicates the        number of streams or the number of layers that the UE can        receive through the same time-frequency resource. The PMI is a        value reflecting a space characteristic of a channel, indicating        an index of a preferred precoding matrix for DL signal        transmission based on a metric such as an SINR. The CQI is a        value of channel strength, indicating a received SINR that can        be obtained by the UE generally when the eNB uses the PMI.

Various PUCCH formats can be used for UCI transmission. UCI carried byone PUCCH may have different size and usage according to PUCCH formats,and size thereof may vary according to coding rates.

A general wireless communication system performs datatransmission/reception through one downlink (DL) band and through oneuplink (UL) band corresponding to the DL band (in case of a frequencydivision duplex (FDD) mode), or divides a prescribed radio frame into aUL time unit and a DL time unit in the time domain and then performsdata transmission/reception through the UL/DL time unit (in case of atime division duplex (TDD) mode). Recently, to use a wider frequencyband in recent wireless communication systems, introduction of carrieraggregation (or BW aggregation) technology that uses a wider UL/DL BW byaggregating a plurality of UL/DL frequency blocks has been discussed. Acarrier aggregation (CA) is different from an orthogonal frequencydivision multiplexing (OFDM) system in that DL or UL communication isperformed using a plurality of carrier frequencies, whereas the OFDMsystem carries a base frequency band divided into a plurality oforthogonal subcarriers on a single carrier frequency to perform DL or ULcommunication. Hereinbelow, each of carriers aggregated by carrieraggregation will be referred to as a component carrier (CC).

For example, three 20 MHz CCs may be aggregated on each of a UL and a DLto support a bandwidth of 60 MHz. The respective CCs may be contiguousor non-contiguous in the frequency domain. For convenience, although ithas been described that the bandwidth of UL CC and the bandwidth of DLCC are the same as each other and symmetric to each other, the bandwidthof each CC may be independently determined. Asymmetrical carrieraggregation in which the number of UL CCs is different from the numberof DL CCs may be implemented. DL/UL CC limited to a specific UE may bereferred to as a serving UL/DL CC configured for the specific UE.

Meanwhile, the 3GPP LTE-A standard uses the concept of a cell to manageradio resources. The “cell” associated with the radio resources isdefined by combination of downlink resources and uplink resources, thatis, combination of DL CC and UL CC. The cell may be configured bydownlink resources only, or may be configured by downlink resources anduplink resources. If carrier aggregation is supported, linkage between acarrier frequency of the downlink resources (or DL CC) and a carrierfrequency of the uplink resources (or UL CC) may be indicated by systeminformation. For example, combination of the DL resources and the ULresources may be indicated by linkage of system information block type 2(SIB2). The carrier frequency means a center frequency of each cell orCC. A cell operating on a primary frequency may be referred to as aprimary cell (Pcell) or PCC, and a cell operating on a secondaryfrequency may be referred to as a secondary cell (Scell) or SCC. Thecarrier corresponding to the Pcell on downlink will be referred to as adownlink primary CC (DL PCC), and the carrier corresponding to the Pcellon uplink will be referred to as an uplink primary CC (UL PCC). A Scellmeans a cell that may be configured after completion of radio resourcecontrol (RRC) connection establishment and used to provide additionalradio resources. The Scell may form a set of serving cells for the UEtogether with the Pcell in accordance with capabilities of the UE. Thecarrier corresponding to the Scell on the downlink will be referred toas downlink secondary CC (DL SCC), and the carrier corresponding to theScell on the uplink will be referred to as uplink secondary CC (UL SCC).Although the UE is in RRC-CONNECTED state, if it is not configured bycarrier aggregation or does not support carrier aggregation, a singleserving cell configured by the Pcell only exists.

The eNB may activate all or some of the serving cells configured in theUE or deactivate some of the serving cells for communication with theUE. The eNB may change the activated/deactivated cell, and may changethe number of cells which is/are activated or deactivated. If the eNBallocates available cells to the UE cell-specifically orUE-specifically, at least one of the allocated cells is not deactivatedunless cell allocation to the UE is fully reconfigured or unless the UEperforms handover. Such a cell which is not deactivated unless CCallocation to the UE is fully reconfigured will be referred to as Pcell,and a cell which may be activated/deactivated freely by the eNB will bereferred to as Scell. The Pcell and the Scell may be discriminated fromeach other on the basis of the control information. For example,specific control information may be set to be transmitted and receivedthrough a specific cell only. This specific cell may be referred to asthe Pcell, and the other cell(s) may be referred to as Scell(s).

A configured cell refers to a cell in which carrier aggregation isperformed for a UE based on measurement report from another eNB or UEamong cells of an eNB and is configured per UE. The cell configured forthe UE may be a serving cell in terms of the UE. For the cell configuredfor the UE, i.e. the serving cell, resources for ACK/NACK transmissionfor PDSCH transmission are reserved in advance. An activated cell refersto a cell configured to be actually used for PDSCH/PUSCH transmissionamong cells configured for the UE and CSI reporting and SRS transmissionfor PDSCH/PUSCH transmission are performed in the activated cell. Adeactivated cell refers to a cell configured not to be used forPDSCH/PUSCH transmission by the command of an eNB or the operation of atimer and, if a cell is deactivated, CSI reporting and SRS transmissionare also stopped in the cell.

For reference, a carrier indicator (CI) denotes a serving cell index(ServCellIndex), CI=0 is applied to Pcell. The serving cell index is ashort ID used to identify a serving cell. For example, any one ofintegers from 0 to ‘maximum number of carrier frequencies which can beconfigured for the UE at a time−1’ may be allocated to one serving cellas the serving cell index. That is, the serving cell index may be alogical index used to identify a specific serving cell among cellsallocated to the UE rather than a physical index used to identify aspecific carrier frequency among all carrier frequencies.

As described above, the term “cell” used in carrier aggregation isdifferentiated from the term “cell” indicating a certain geographicalarea where a communication service is provided by one eNB or one antennagroup.

The cell mentioned in the present invention means a cell of carrieraggregation which is combination of UL CC and DL CC unless specificallynoted.

Meanwhile, since one serving cell is only present in case ofcommunication based on a single carrier, a PDCCH carrying UL/DL grantand corresponding PUSCH/PDSCH are transmitted on one cell. In otherwords, in case of FDD under a single carrier environment, a PDCCH for aDL grant for a PDSCH, which will be transmitted on a specific DL CC, istransmitted on the specific CC, and a PDCCH for a UL grant for a PUSCH,which will be transmitted on a specific UL CC, is transmitted on a DL CClinked to the specific UL CC. In case of TDD under a single carrierenvironment, a PDCCH for a DL grant for a PDSCH, which will betransmitted on a specific DL CC, is transmitted on the specific CC, anda PDCCH for a UL grant for a PUSCH, which will be transmitted on aspecific UL CC, is transmitted on the specific CC.

On the other hand, since a plurality of serving cells can be configuredin a multi-carrier system, transmission of UL/DL grant through a servingcell having a good channel state may be allowed. In this way, when acell carrying UL/DL grant corresponding to scheduling information isdifferent from that where UL/DL transmission corresponding to the UL/DLgrant is performed, it can be referred to as cross-carrier scheduling.

Hereinafter, the case where a cell is scheduled by itself and the casewhere a cell is scheduled by another cell will be respectively referredto as self-CC scheduling and cross-CC scheduling.

The 3GPP LTE/LTE-A system can support aggregation of a plurality of CCsand cross carrier-scheduling operation based on the aggregation toimprove a data transmission rate and achieve stable control signaling.

When the cross-carrier scheduling (or cross-CC scheduling) is applied, aPDCCH carrying a DL grant, that is, downlink allocation for DL CC B orDL CC C may be transmitted through DL CC A, and a corresponding PDSCHmay be transmitted through DL CC B or DL CC C. In addition, a carrierindicator field (CIF) may be introduced for the cross-CC scheduling. TheCIF can be included or not in the PDCCH, and this can be configuredthrough higher layer signaling (e.g., RRC signaling) semi-statically andUE-specifically (or UE-group-specifically). In legacy systems subject tocommunication with one node, the UE-RS, CSI-RS, and CRS are transmittedat the same location, and therefore the UE does not consider a situationin which delay spread, Doppler spread, frequency shift, average receivedpower, and received timing differ among the UE-RS port(s), CSI-RSport(s) and CRS port(s0. However, for a communication system to whichcoordinated Multi-Point (CoMP) communication technology allowing morethan one node to simultaneously participate in communication with the UEis applied, the properties may differ among the PDCCH port(s), PDSCHport(s), UE-RS port(s), CSI-RS port(s) and/or CRS port(s). For thisreason, the concept of a “quasi co-located antenna port” is introducedfor a mode (hereinafter, CoMP mode) in which multiple nodes canparticipate in communication.

With respect to antenna ports, the term “Quasi co-located (QCL)” or“quasi co-location (QCL)” can be defined as follows: if two antennaports are QCL, the UE may assume that the large-scale properties of asignal received through one of the two antenna ports can be inferredfrom the signal received through the other antenna port. The large-scaleproperties include delay spread, Doppler spread, frequency shift,average received power and/or received timing.

With respect to channels, the term QCL may also be defined as follows:if two antenna ports are QCL, the UE may assume that the large-scaleproperties of a channel for conveying a symbol on one of the two antennaports can be inferred from the large-scale properties of a channel forconveying a symbol on the other antenna port. The large-scale propertiesinclude delay spread, Doppler spread, Doppler shift, average gain and/oraverage delay.

One of the two definitions of QCL given above may be applied to theembodiments of the present invention. Alternatively, the definition ofQCL may be modified to assume that antenna ports for which QCLassumption is established are co-located. For example, QCL may bedefined in a manner that the UE assumes that the antenna ports for whichQCL assumption is established are antenna ports of the same transmissionpoint.

For non-quasi co-located (NQC) antenna ports, the UE cannot assume thesame large-scale properties between the antenna ports. A typical UEneeds to perform independent processing for each NQC antenna withrespect to timing acquisition and tracking, frequency offset estimationand compensation, and delay estimation and Doppler estimation.

On the other hand, for antenna ports for which QCL assumption can beestablished, the UE performs the following operations:

Regarding Doppler spread, the UE may apply the results of estimation ofthe power-delay-profile, the delay spread and Doppler spectrum and theDoppler spread for one port to a filter (e.g., a Wiener filter) which isused for channel estimation for another port;

Regarding frequency shift and received timing, after performing time andfrequency synchronization for one port, the UE may apply the samesynchronization to demodulation on another port;

Further, regarding average received power, the UE may averagemeasurements of reference signal received power (RSRP) over two or moreantenna ports.

For example, if the UE receives a specific DMRS-based DL-related DCIformat (e.g., DCI format 2C) over a PDCCH/EPDCCH, the UE performs datademodulation after performing channel estimation of the PDSCH through aconfigured DMRS sequence. If the UE can make an assumption that a DMRSport configuration received through the DL scheduling grant and a portfor a specific RS (e.g., a specific CSI-RS, a specific CRS, a DL servingcell CRS of the UE, etc.) port are QCL, then the UE may apply theestimate(s) of the large-scale properties estimated through the specificRS port to channel estimation through the DMRS port, thereby improvingprocessing performance of the DMRS-based receiver.

FIG. 5 illustrates configuration of cell specific reference signals(CRSs) and user specific reference signals (UE-RS). In particular, FIG.5 shows REs occupied by the CRS(s) and UE-RS(s) on an RB pair of asubframe having a normal CP.

In an existing 3GPP system, since CRSs are used for both demodulationand measurement, the CRSs are transmitted in all DL subframes in a cellsupporting PDSCH transmission and are transmitted through all antennaports configured at an eNB.

Referring to FIG. 5, the CRS is transmitted through antenna ports p=0,p=0, 1, p=0, 1, 2, 3 in accordance with the number of antenna ports of atransmission mode. The CRS is fixed to a certain pattern within asubframe regardless of a control region and a data region. The controlchannel is allocated to a resource of the control region, to which theCRS is not allocated, and the data channel is also allocated to aresource of the data region, to which the CRS is not allocated.

A UE may measure CSI using the CRSs and demodulate a signal received ona PDSCH in a subframe including the CRSs. That is, the eNB transmits theCRSs at predetermined locations in each RB of all RBs and the UEperforms channel estimation based on the CRSs and detects the PDSCH. Forexample, the UE may measure a signal received on a CRS RE and detect aPDSCH signal from an RE to which the PDSCH is mapped using the measuredsignal and using the ratio of reception energy per CRS RE to receptionenergy per PDSCH mapped RE. However, when the PDSCH is transmitted basedon the CRSs, since the eNB should transmit the CRSs in all RBs,unnecessary RS overhead occurs. To solve such a problem, in a 3GPP LTE-Asystem, a UE-specific RS (hereinafter, UE-RS) and a CSI-RS are furtherdefined in addition to a CRS. The UE-RS is used for demodulation and theCSI-RS is used to derive CSI. The UE-RS is one type of DRS. Since theUE-RS and the CRS are used for demodulation, the UE-RS and the CRS maybe regarded as demodulation RSs in terms of usage. Since the CSI-RS andthe CRS are used for channel measurement or channel estimation, theCSI-RS and the CRS may be regarded as measurement RSs.

Referring to FIG. 5, UE-RSs are transmitted on antenna port(s) p=5, p=7,p=8 or p=7, 8, . . . , υ+6 for PDSCH transmission, where v is the numberof layers used for the PDSCH transmission. UE-RSs are present and are avalid reference for PDSCH demodulation only if the PDSCH transmission isassociated with the corresponding antenna port. UE-RSs are transmittedonly on RBs to which the corresponding PDSCH is mapped. That is, theUE-RSs are configured to be transmitted only on RB(s) to which a PDSCHis mapped in a subframe in which the PDSCH is scheduled unlike CRSsconfigured to be transmitted in every subframe irrespective of whetherthe PDSCH is present. Accordingly, overhead of the RS may be loweredcompared to that of the CRS.

In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair.Referring to FIG. 5, in a PRB having frequency-domain index n_(PRB)assigned for PDSCH transmission with respect to p=7, p=8, or p=7, 8, . .. , υ+6, a part of UE-RS sequence r(m) is mapped to complex-valuedmodulation symbols a^((p)) _(k,l) in a subframe according to thefollowing equation.a _(k,l) ^((p)) w _(p)(l′)·r(3·l′·N _(RB) ^(max,DL)+3·n _(PRB)+m′)  Equation 1

where w_(p)(i), l′, m′ are given as follows.

Equation 2

$\mspace{20mu}{{w_{p}(i)} = \left\{ {{\begin{matrix}{{\overset{\_}{w}}_{p}(i)} & {{\left( {m^{\prime} + n_{PRB}} \right){mod}\; 2} = 0} \\{{\overset{\_}{w}}_{p}\left( {3 - i} \right)} & {{\left( {m^{\prime} + n_{PRB}} \right){mod}\; 2} = 1}\end{matrix}\mspace{20mu} k} = {{{5m^{\prime}} + {N_{sc}^{RB}n_{PRB}} + {k^{\prime}\mspace{20mu} k^{\prime}}} = \left\{ {{\begin{matrix}1 & {p \in \left\{ {7,8,11,13} \right\}} \\0 & {p \in \left\{ {9,10,12,14} \right\}}\end{matrix}l} = \left\{ {{\begin{matrix}{{l^{\prime}{mod}\; 2} + 2} & {{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{specialsubframewith}\mspace{14mu}{configuration}} \\\; & {3,4,{{or}\mspace{14mu} 8\mspace{11mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}} \\{{l^{\prime}{mod}\; 2} + 2 + {3\left\lfloor {l^{\prime}/2} \right\rfloor}} & {{if}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{specialsubframewith}\mspace{14mu}{configuration}} \\\; & {1,2,6,{{or}\mspace{14mu} 7\mspace{11mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}} \\{{l^{\prime}{mod}\; 2} + 5} & {{if}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu} a\mspace{14mu}{specialsubframe}}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}{0,1,2,3} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\; 2} = {0\mspace{14mu}{and}\mspace{14mu}{in}\mspace{14mu} a\mspace{20mu}{specialsubframewith}}} \\\; & {{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{11mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}} \\{0,1} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\; 2} = {0\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu}{specialsubframewith}}} \\\; & {{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{11mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}} \\{2,3} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\; 2} = {1\mspace{14mu}{and}\mspace{14mu}{not}\mspace{14mu}{in}\mspace{14mu}{specialsubframewith}}} \\\; & {{{configuration}\mspace{14mu} 1},2,6,{{or}\mspace{14mu} 7\mspace{11mu}\left( {{see}\mspace{14mu}{Table}\mspace{14mu} 2} \right)}}\end{matrix}\mspace{20mu} m^{\prime}} = 0},1,2} \right.} \right.} \right.}} \right.}$

where n_(s) is the slot number within a radio frame and an integer among0 to 19. The sequence w _(p)(i) for normal CP is given according to thefollowing equation.

TABLE 7 Antenna port p [w _(p) ⁽⁰⁾ w _(p) ⁽¹⁾ w _(p) ⁽²⁾ w _(p) ⁽³⁾ ] 7[+1 +1 +1 +1] 8 [+1 −1 +1 −1] 9 [+1 +1 +1 +1] 10 [+1 −1 +1 −1] 11 [+1 +1−1 −1] 12 [−1 −1 +1 +1] 13 [+1 −1 −1 +1] 14 [−1 +1 +1 −1]

For antenna port p∈{7, 8, . . . , υ+6}, the UE-RS sequence r(m) isdefined as follows.

$\begin{matrix}{\mspace{79mu}{{{r(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}},{m = \left\{ \begin{matrix}{0,1,\ldots\mspace{14mu},{{12N_{RB}^{{{ma}\; x},{DL}}} - 1}} & {{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}} \\{0,1,\ldots\mspace{14mu},{{16N_{RB}^{{{ma}\; x},{DL}}} - 1}} & {{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \right.}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

where c(i) is a pseudo-random sequence defined by a length−31 Goldsequence. The output sequence c(n) of length M_(PN), where n=0, 1, . . ., M_(PN)−1, is defined by the following equation.c(n)=(x ₁(n+N _(C))+x ₂(n+N _(C))mod 2x ₁(n+31)=(x ₁(n+3)+x ₁(n))mod 2x ₂(n+31)=(x ₂(n+3)+x ₂(n+2)+x ₂(n+1)+x ₂(n))mod 2  Equation 4

where N_(C)=1600 and the first m-sequence is initialized with x₁(0)=1,x₁(n)=0, n=1, 2, . . . , 30. The initialization of the second m-sequenceis denoted by c_(init)=Σ_(i=0) ³⁰ x₂(i)·2^(i) with the value dependingon the application of the sequence.

In Equation 3, the pseudo-random sequence generator for generating c(i)is initialized with c_(init) at the start of each subframe according tothe following equation.c _(init)=(└n _(s)/2┘+1)·(2n _(ID) ^((n) ^(SCID) ⁾+1)·2¹⁶ +n_(SCID)  Equation 5

where the quantities n^((i)) _(ID), i=0, 1, which is corresponding ton^((nSCID)) _(ID), are given by a physical layer cell identity N^(cell)_(ID) if no value for a scrambling identity n^(DMRS,i) _(ID) is providedby higher layers or if DCI format 1A, 2B or 2C is used for DCI formatassociated with the PDSCH transmission, and given by n^(DMRS,i) _(ID)otherwise.

In Math FIG. 5, the value of n_(sCID) is zero unless specifiedotherwise. For a PDSCH transmission on antenna ports 7 or 8, n_(sCID) isgiven by the DCI format 2B or 2C. DCI format 2B is a DCI format forresource assignment for a PDSCH using a maximum of two antenna portshaving UE-RSs. DCI format 2C is a DCI format for resource assignment fora PDSCH using a maximum of 8 antenna ports having UE-RSs.

FIG. 6 is an example of a downlink control channel configured in a dataregion of a DL subframe.

Meanwhile, if RRH technology, cross-carrier scheduling technology, etc.are introduced, the amount of PDCCH which should be transmitted by theeNB is gradually increased. However, since a size of a control regionwithin which the PDCCH may be transmitted is the same as before, PDCCHtransmission acts as a bottleneck of system throughput. Although channelquality may be improved by the introduction of the aforementionedmulti-node system, application of various communication schemes, etc.,the introduction of a new control channel is required to apply thelegacy communication scheme and the carrier aggregation technology to amulti-node environment. Due to the need, a configuration of a newcontrol channel in a data region (hereinafter, referred to as PDSCHregion) not the legacy control region (hereinafter, referred to as PDCCHregion) has been discussed. Hereinafter, the new control channel will bereferred to as an enhanced PDCCH (hereinafter, referred to as EPDCCH).

The EPDCCH may be configured within rear OFDM symbols starting from aconfigured OFDM symbol, instead of front OFDM symbols of a subframe. TheEPDCCH may be configured using continuous frequency resources, or may beconfigured using discontinuous frequency resources for frequencydiversity. By using the EPDCCH, control information per node may betransmitted to a UE, and a problem that a legacy PDCCH region may not besufficient may be solved. For reference, the PDCCH may be transmittedthrough the same antenna port(s) as that(those) configured fortransmission of a CRS, and a UE configured to decode the PDCCH maydemodulate or decode the PDCCH by using the CRS. Unlike the PDCCHtransmitted based on the CRS, the EPDCCH is transmitted based on thedemodulation RS (hereinafter, DMRS). Accordingly, the UEdecodes/demodulates the PDCCH based on the CRS and decodes/demodulatesthe EPDCCH based on the DMRS. The DMRS associated with EPDCCH istransmitted on the same antenna port p∈{107, 108, 109, 110} as theassociated EPDCCH physical resource, is present for EPDCCH demodulationonly if the EPDCCH transmission is associated with the correspondingantenna port, and is transmitted only on the PRB(s) upon which thecorresponding EPDCCH is mapped. For example, the REs occupied by theUE-RS(s) of the antenna port 7 or 8 may be occupied by the DMRS(s) ofthe antenna port 107 or 108 on the PRB to which the EPDCCH is mapped,and the REs occupied by the UE-RS(s) of antenna port 9 or 10 may beoccupied by the DMRS(s) of the antenna port 109 or 110 on the PRB towhich the EPDCCH is mapped. In other words, a certain number of REs areused on each RB pair for transmission of the DMRS for demodulation ofthe EPDCCH regardless of the UE or cell if the type of EPDCCH and thenumber of layers are the same as in the case of the UE-RS fordemodulation of the PDSCH.

For each serving cell, higher layer signaling can configure a UE withone or two EPDCCH-PRB-sets for EPDCCH monitoring. The PRB-pairscorresponding to an EPDCCH-PRB-set are indicated by higher layers. EachEPDCCH-PRB-set consists of set of ECCEs numbered from 0 toN_(ECCE,p,k)−1, where N_(ECCE,p,k) is the number of ECCEs inEPDCCH-PRB-set p of subframe k. Each EPDCCH-PRB-set can be configuredfor either localized EPDCCH transmission or distributed EPDCCHtransmission.

The UE shall monitor a set of EPDCCH candidates on one or more activatedserving cells as configured by higher layer signaling for controlinformation.

The set of EPDCCH candidates to monitor are defined in terms of EPDCCHUE-specific search spaces. For each serving cell, the subframes in whichthe UE monitors EPDCCH UE-specific search spaces are configured byhigher layers.

An EPDCCH UE-specific search space ES^((L)) _(k) at aggregation levelL∈{1, 2, 4, 8, 16, 32} is defined by a set of EPDCCH candidates. For anEPDCCH-PRB-set p, the ECCEs corresponding to EPDCCH candidate m of thesearch space ES^((L)) _(k) are given by the following equation.

$\begin{matrix}{{L\left\{ {\left( {Y_{p,k} + \left\lfloor \frac{m \cdot N_{{ECCE},p,k}}{L \cdot M_{p}^{(L)}} \right\rfloor + b} \right){mod}\left\lfloor {N_{{ECCE},p,k}/L} \right\rfloor} \right\}} + i} & {{Equation}\mspace{14mu} 6}\end{matrix}$

where i=0, . . . , L−1. b=n_(CI) if the UE is configured with a carrierindicator field for the serving cell on which EPDCCH is monitored,otherwise b=0. n_(CI) is the carrier indicator field (CIF) value, whichis the same as a serving cell index (ServCellIndex). m=0, 1, . . . ,M^((L)) _(p)−1, M^((L)) _(p) is the number of EPDCCH candidates tomonitor at aggregation level L in EPDDCH-PRB-set p. The variable Y_(p,k)is defined by ‘Y_(p,k)=(A_(p)·Y_(p,k-1)) mod D’, whereY_(p,k-1)=n_(RNTI)0, A₀=39827, A₀=39829, D=65537 and k=floor(n_(s)/2).n_(s) is the slot number within a radio frame.

A UE is not expected to monitor an EPDCCH candidate, if an ECCEcorresponding to that EPDCCH candidate is mapped to a PRB pair thatoverlaps in frequency with a transmission of either PBCH or PSS/SSS inthe same subframe.

An EPDCCH is transmitted using an aggregation of one or severalconsecutive enhanced control channel elements (ECCEs). Each ECCEconsists of multiple enhanced resource element groups (EREGs). EREGs areused for defining the mapping of enhanced control channels to resourceelements. There are 16 EREGs, numbered from 0 to 15, per physicalresource block (PRB) pair. Number all resource elements (REs), exceptresource elements carrying DMRS (hereinafter, EPDCCH DMRS) fordemodulation of the EPDCCH, in a physical resource-block pair cyclicallyfrom 0 to 15 in an increasing order of first frequency. Therefore, allthe REs, except REs carrying the EPDCCH DMRS, in the PRB pair has anyone of numbers 0 to 15. All REs with number i in that PRB pairconstitutes EREG number i. As described above, it is noted that EREGsare distributed on frequency and time axes within the PRB pair and anEPDCCH transmitted using aggregation of one or more ECCEs, each of whichincludes a plurality of EREGs, is also distributed on frequency and timeaxes within the PRB pair.

The number of ECCEs used for one EPDCCH depends on the EPDCCH format asgiven by Table 8, the number of EREGs per ECCE is given by Table 9.Table 8 shows an example of supported EPDCCH formats, and Table 9 showsan example of the number of EREGs per ECCE, N^(EREG) _(ECCE). Bothlocalized and distributed transmission is supported.

TABLE 8 Number of ECCEs for one EPDCCH, N^(EPDCCH) _(ECCE) Case A Case BEPDCCH Localized Distributed Localized Distributed format transmissiontransmission transmission transmission 0 2 2 1 1 1 4 4 2 2 2 8 8 4 4 316  16 8 8 4 — 32 — 16

TABLE 9 Normal cyclic prefix Special Special subframe, Extended cyclicprefix subframe, configuration Special subframe, Normal configuration 1,2, 6, Normal configuration subframe 3, 4, 8 7, 9 subframe 1, 2, 3, 5, 64 8

An EPDCCH can use either localized or distributed transmission,differing in the mapping of ECCEs to EREGs and PRB pairs. One or twosets of PRB pairs which a UE shall monitor for EPDCCH transmissions canbe configured. All EPDCCH candidates in EPDCCH set S_(p) (i.e.,EPDCCH-PRB-set) use either only localized or only distributedtransmission as configured by higher layers. Within EPDCCH set S_(p) insubframe k, the ECCEs available for transmission of EPDCCHs are numberedfrom 0 to N_(ECCE,p,k)−1. ECCE number n is corresponding to thefollowing EREG(s):

-   -   EREGs numbered (n mod N^(ECCE) _(RB))+jN^(ECCE) _(RB) in PRB        index floor(n/N^(ECCE) _(RB)) for localized mapping, and    -   EREGs numbered floor (n/N^(Sm) _(RB))+jN^(ECCE) _(RB) in PRB        indices (n+jmax(1,N^(sP) _(RB)/N^(EREG) _(ECCE)))mod N^(sp)        _(RB) for distributed mapping,

where j=0, 1, . . . , N^(EREG) _(ECCE)−1, N^(EREG) _(ECCE) is the numberof EREGs per ECCE, and N^(ECCE) _(RB)=16/N^(EREG) _(ECCE) is the numberof ECCEs per RB pair. The PRB pairs constituting EPDCCH set S_(p) areassumed to be numbered in ascending order from 0 to N^(Sp) _(RB)−1.

Case A in Table 8 applies when:

-   -   DCI formats 2, 2A, 2B, 2C or 2D is used and N^(DL) _(RB)≥25, or    -   any DCI format when n_(EPDCCH)<104 and normal cyclic prefix is        used in normal subframes or special subframes with configuration        3, 4, 8.

Otherwise case 2 is used. The quantity n_(EPDCCH) for a particular UE isdefined as the number of downlink resource elements (k,l) in a PRB pairconfigured for possible EPDCCH transmission of EPDCCH set S₀ and andfulfilling all of the following criteria,

-   -   they are part of any one of the 16 EREGs in the physical        resource-block pair,    -   they are assumed by the UE not to be used for CRSs or CSI-RSs,    -   the index l in a subframe fulfils l≥l_(EPDCCHStart).

where l_(EPDCCHStart) is given based on higher layer signaling‘epdcch-StartSymbol-r11’, higher layer signaling ‘pdsch-Start-r11’, orCFI value carried by PCFICH.

The mapping to resource elements (k,l) on antenna port p meeting thecriteria above is in increasing order of first the index k and then theindex l, starting with the first slot and ending with the second slot ina subframe.

For localized transmission, the single antenna port p to use is given byTable 12 with n′=n_(ECCE,low) mod N^(ECCE) _(RB+n) _(RNTI) modmin(N^(ECCE) _(EPDCCH), N^(ECCE) _(RB)) where n_(ECCE,low) is the lowestECCE index used by this EPDCCH transmission in the EPDCCH set, n_(RNTI)corresponds to the RNTI associated with the EPDCCH transmission, andN^(ECCE) _(EPDCCH) is the number of ECCEs used for this EPDCCH.

TABLE 10 Normal cyclic prefix Extended cyclic prefix Normal subframes,Special subframes, Special subframes, Special subframes, configurationsNormal subframes, n′ configurations 3, 4, 8 1, 2, 6, 7, 9 configurations3, 4, 8 0 107 107 107 1 108 109 108 2 109 — — 4 110 — —

For distributed transmission, each resource element in an EREG isassociated with one out of two antenna ports in an alternating mannerwhere p∈{107, 109} for normal cyclic prefix and p∈{107, 108} forextended cyclic prefix.

Hereinafter, the PDCCH and EPDCCH will be commonly referred to as thePDCCH or (E)PDCCH.

Recently, machine type communication (MTC) has come to the fore as asignificant communication standard issue. MTC refers to exchange ofinformation between a machine and an eNB without involving persons orwith minimal human intervention. For example, MTC may be used for datacommunication for measurement/sensing/reporting such as meter reading,water level measurement, use of a surveillance camera, inventoryreporting of a vending machine, etc. and may also be used for automaticapplication or firmware update processes for a plurality of UEs. In MTC,the amount of transmission data is small and UL/DL data transmission orreception (hereinafter, transmission/reception) occurs occasionally. Inconsideration of such properties of MTC, it would be better in terms ofefficiency to reduce production cost and battery consumption of UEs forMTC (hereinafter, MTC UEs) according to data transmission rate. Sincethe MTC UE has low mobility, the channel environment thereof remainssubstantially the same. If an MTC UE is used for metering, reading of ameter, surveillance, and the like, the MTC UE is very likely to belocated in a place such as a basement, a warehouse, and mountain regionswhich the coverage of a typical eNB does not reach. In consideration ofthe purposes of the MTC UE, it is better for a signal for the MTC UE tohave wider coverage than the signal for the conventional UE(hereinafter, a legacy UE).

When considering the usage of the MTC UE, there is a high probabilitythat the MTC UE requires a signal of wide coverage compared with thelegacy UE. Therefore, if the eNB transmits a PDCCH, a PDSCH, etc. to theMTC UE using the same scheme as a scheme of transmitting the PDCCH, thePDSCH, etc. to the legacy UE, the MTC UE has difficulty in receiving thePDCCH, the PDSCH, etc. Therefore, the present invention proposes thatthe eNB apply a coverage enhancement scheme such as subframe repetition(repetition of a subframe with a signal) or subframe bundling upontransmission of a signal to the MTC UE having a coverage issue so thatthe MTC UE can effectively receive a signal transmitted by the eNB. Forexample, the PDCCH and PDSCH may be transmitted to the MTC UE having thecoverage issue in a plurality of subframes (e.g. about 100 subframes).

The embodiments of the present invention can be applied to not only the3GPP LTE/LTE-A system but also a new radio access technology (RAT)system. As a number of communication devices have required much highercommunication capacity, the necessity of mobile broadband communication,which is much enhanced compared to the conventional RAT, has increased.In addition, massive MTC capable of providing various services anytimeand anywhere by connecting a number of devices or things to each otherhas been considered as a main issue in the next generation communicationsystem. Moreover, the design of a communication system capable ofsupporting services/UEs sensitive to reliability and latency has alsobeen discussed. That is, the introduction of the next generation RATconsidering the enhanced mobile broadband communication, massive MTC,Ultra-reliable and low latency communication (URLLC), etc. has beendiscussed. For convenience of description, the corresponding technologyis simply referred to as a new RAT in this specification.

In the next system of LTE-A, a method to reduce latency of datatransmission is considered. Packet data latency is one of theperformance metrics that vendors, operators and also end-users (viaspeed test applications) regularly measure. Latency measurements aredone in all phases of a radio access network system lifetime, whenverifying a new software release or system component, when deploying asystem and when the system is in commercial operation.

Better latency than previous generations of 3GPP RATs was oneperformance metric that guided the design of LTE. LTE is also nowrecognized by the end-users to be a system that provides faster accessto internet and lower data latencies than previous generations of mobileradio technologies.

However, with respect to further improvements specifically targeting thedelays in the system little has been done. Packet data latency isimportant not only for the perceived responsiveness of the system; it isalso a parameter that indirectly influences the throughput. HTTP/TCP isthe dominating application and transport layer protocol suite used onthe internet today. According to HTTP Archive(http://httparchive.org/trends.php) the typical size of HTTP-basedtransactions over the internet are in the range from a few 10's ofKbytes up to 1 Mbyte. In this size range, the TCP slow start period is asignificant part of the total transport period of the packet stream.During TCP slow start the performance is latency limited. Hence,improved latency can rather easily be shown to improve the averagethroughput, for this type of TCP-based data transactions. In addition,to achieve really high bit rates (in the range of Gbps), UE L2 buffersneed to be dimensioned correspondingly. The longer the round trip time(RTT) is, the bigger the buffers need to be. The only way to reducebuffering requirements in the UE and eNB side is to reduce latency.

Radio resource efficiency could also be positively impacted by latencyreductions. Lower packet data latency could increase the number oftransmission attempts possible within a certain delay bound; hencehigher block error ration (BLER) targets could be used for the datatransmissions, freeing up radio resources but still keeping the samelevel of robustness for users in poor radio conditions. The increasednumber of possible transmissions within a certain delay bound, couldalso translate into more robust transmissions of real-time data streams(e.g. VoLTE), if keeping the same BLER target. This would improve theVoLTE voice system capacity.

There are more over a number of existing applications that would bepositively impacted by reduced latency in terms of increased perceivedquality of experience: examples are gaming, real-time applications likeVoLTE/OTT VoIP and video telephony/conferencing.

Going into the future, there will be a number of new applications thatwill be more and more delay critical. Examples include remotecontrol/driving of vehicles, augmented reality applications in e.g.smart glasses, or specific machine communications requiring low latencyas well as critical communications.

In embodiments of the present invention described below, the term“assume” may mean that a subject to transmit a channel transmits thechannel in accordance with the corresponding “assumption.” This may alsomean that a subject to receive the channel receives or decodes thechannel in a form conforming to the “assumption,” on the assumption thatthe channel has been transmitted according to the “assumption.”

FIG. 7 illustrates the length of a transmission time interval (TTI)which is needed to implement low latency.

Referring to FIG. 7, a propagation delay (PD), a buffering time, adecoding time, an A/N preparation time, an uplink PD, and an OTA (overthe air) delay according to a retransmission margin are produced while asignal transmitted from the eNB reaches the UE, the UE transmits an A/Nfor the signal, and the A/N reaches the eNB. To satisfy low latency, ashortened TTI (sTTI) shorter than or equal to 0.5 ms needs to bedesigned by shortening the TTI, which is the smallest unit of datatransmission. For example, to shorten the OTA delay, which is a timetaken from the moment the eNB starts to transmit data (PDCCH and PDSCH)until the UE completes transmission of an A/N for the data to the eNB,to a time shorter than 1 ms, the TTI is preferably set to 0.21 ms. Thatis, to shorten the user plane (U-plane) delay to 1 ms, the sTTI may beset in the unit of about three OFDM symbols.

While FIG. 7 illustrates that the sTTI is configured with three OFDMsymbols to satisfy 1 ms as the OTA delay or U-plane delay, an sTTIshorter than 1 ms may also be configured. For example, for the normalCP, an sTTI consisting of 2 OFDM symbols, an sTTI consisting of 4 OFDMsymbols and/or an sTTI consisting of 7 OFDM symbols may be configured.

In the time domain, all OFDM symbols constituting a default TTI or theOFDM symbols except the OFDM symbols occupying the PDCCH region of theTTI may be divided into two or more sTTIs on some or all frequencyresources in the frequency band of the default TTI.

In the following description, a default TTI or main TTI used in thesystem is referred to as a TTI or subframe, and the TTI having a shorterlength than the default/main TTI of the system is referred to as ansTTI. For example, in a system in which a TTI of 1 ms is used as thedefault TTI as in the current LTE/LTE-A system, a TTI shorter than 1 msmay be referred to as the sTTI. In addition, in the followingdescription, a physical downlink control channel/physical downlink datachannel/physical uplink control channel/physical uplink data channeltransmitted in units of the default/main TTI are referred to as aPDCCH/PDSCH/PUCCH/PUSCH, and a PDCCH/PDSCH/PUCCH/PUSCH transmittedwithin an sTTI or in units of sTTI are referred to assPDCCH/sPDSCH/sPUCCH/sPUSCH. In the new RAT environment, the numerologymay be changed, and thus a default/main TTI different from that for thecurrent LTE/LTE-A system may be used. However, for simplicity, thedefault/main TTI will be referred to as a TTI, subframe, legacy TTI orlegacy subframe, and a TTI shorter than 1 ms will be referred to as ansTTI, on the assumption that the time length of the default/main TTI is1 ms. The method of transmitting/receiving a signal in a TTI and an sTTIaccording to embodiments described below is applicable not only to thesystem according to the current LTE/LTE-A numerology but also to thedefault/main TTI and sTTI of the system according to the numerology forthe new RAT environment.

FIG. 8 illustrates an sTTI and transmission of a control channel anddata channel within the sTTI.

In the downlink environment, a PDCCH for transmission/scheduling of datawithin an sTTI (i.e., sPDCCH) and a PDSCH transmitted within an sTTI(i.e., sPDSCH) may be transmitted. For example, referring to FIG. 8, aplurality of the sTTIs may be configured within one subframe, usingdifferent OFDM symbols. For example, the OFDM symbols in the subframemay be divided into one or more sTTIs in the time domain. OFDM symbolsconstituting an sTTI may be configured, excluding the leading OFDMsymbols on which the legacy control channel is transmitted. Transmissionof the sPDCCH and sPDSCH may be performed in a TDM manner within thesTTI, using different OFDM symbol regions. In an sTTI, the sPDCCH andsPDSCH may be transmitted in an FDM manner, using different regions ofPRB(s)/frequency resources.

The present invention is directed to a method of providing a pluralityof different services in one system by applying different systemparameters according to the services or UEs to satisfy the requirementsfor the services. In particular, for a service/UE sensitive to latency,an sTTI may be used to send data in a short time and to allow a responseto the data to be sent in a short time. Thereby, the latency may bereduced as much as possible. On the other hand, for a service/UE whichis less sensitive to latency, a longer TTI may be used totransmit/receive data. For a service/UE which is sensitive to powerefficiency rather than to latency, data may be repeatedly transmitted atthe same low power or may be transmitted in units of a longer TTI. Thepresent invention proposes a transmission method and multiplexing methodfor controlling information and data signals to enable the operationsdescribed above. The proposed methods are associated with thetransmission aspect of a network, the reception aspect of a UE,multiplexing of multiple TTIs in one UE, and multiplexing of multipleTTIs between multiple UEs.

FIG. 9 illustrates an example of short TTIs configured in a legacysubframe.

In legacy LTE/LTE-A, if a subframe of 1 ms has a normal CP, the subframeconsists of 14 OFDM symbols. If a TTI shorter than 1 ms is configured, aplurality of TTIs may be configured within one subframe. As shown inFIG. 9, each TTI may consist of, for example, 2 symbols, 3 symbols, 4symbols, or 7 symbols. Although not shown in FIG. 9, a TTI consisting ofone symbol may also be considered. If one symbol is one TTI unit, 12TTIs may be configured in the default TTI of 1 ms, on the assumptionthat the legacy PDCCH is transmittable within two OFDM symbols.Similarly, when the two leading OFDM symbols are assumed to be thelegacy PDCCH region, and two symbols are taken as one TTI unit, 6 TTIsmay be configured within the default TTI. If three symbols are taken asone TTI, 4 TTIs may be configured within the default TTI. If 4 symbolsare taken as one TTI unit, 3 TTIs may be configured within the defaultTTI.

If the 7 symbols are configured as one TTI, a TTI consisting of 7leading symbols including the legacy PDCCH region and a TTI consistingof 7 subsequent symbols may be configured. If one TTI consists of 7symbols, a UE supporting the short TTI assumes that the two leading OFDMsymbols on which the legacy PDCCH is transmitted are punctured orrate-matched and the data and/or control channels of the UE aretransmitted on the five subsequent symbols in the TTI (i.e., the TTI ofthe first slot) positioned at the leading part of one subframe (i.e.,default TTI). On the other hand, the UE may assume that the data and/orcontrol channels can be transmitted on all 7 symbols in a TTI positionedat the rear part of the same subframe (i.e., the TTI of the second slot)without any rate-matched or punctured resource region.

Puncturing a channel on a specific resource means that the signal of thechannel is mapped to the specific resource in the procedure of resourcemapping of the channel, but a portion of the signal mapped to thepunctured resource is excluded in transmitting the channel. In otherwords, the specific resource which is punctured is counted as a resourcefor the channel in the procedure of resource mapping of the channel, asignal mapped to the specific resource among the signals of the channelis not actually transmitted. The receiver of the channel receives,demodulates or decodes the channel, assuming that the signal mapped tothe specific resource is not transmitted. On the other hand,rate-matching of a channel on a specific resource means that the channelis never mapped to the specific resource in the procedure of resourcemapping of the channel, and thus the specific resource is not used fortransmission of the channel. In other words, the rate-matched resourceis not counted as a resource for the channel in the procedure ofresource mapping of the channel. The receiver of the channel receives,demodulates, or decodes the channel, assuming that the specificrate-matched resource is not used for mapping and transmission of thechannel.

<OFDM Numerology>

The new RAT system uses an OFDM transmission scheme or a similartransmission scheme. For example, the new RAT system may follow the OFDMparameters defined in the following table.

TABLE 11 Parameter Value Subcarrier-spacing (Δf) 75 kHz OFDM symbollength 13.33 us Cyclic Prefix(CP) length 1.04 us/0/94 us System BW 100MHz No. of available subcarriers 1200 Subframe length 0.2 ms Number ofOFDM symbol per 14 symbols Subframe

<Self-Contained Subframe Structure>

FIG. 10 illustrates a self-contained subframe structure.

In order to minimize the latency of data transmission in the TDD system,a self-contained subframe structure is considered in the newfifth-generation RAT.

In FIG. 10, the hatched area represents the transmission region of a DLcontrol channel (e.g., PDCCH) carrying the DCI, and the black arearepresents the transmission region of a UL control channel (e.g., PUCCH)carrying the UCI. Here, the DCI is control information that the eNBtransmits to the UE. The DCI may include information on cellconfiguration that the UE should know, DL specific information such asDL scheduling, and UL specific information such as UL grant. The UCI iscontrol information that the UE transmits to the eNB. The UCI mayinclude a HARQ ACK/NACK report on the DL data, a CSI report on the DLchannel status, and a scheduling request (SR).

In FIG. 10, the region of symbols from symbol index 1 to symbol index 12may be used for transmission of a physical channel (e.g., a PDSCH)carrying downlink data, or may be used for transmission of a physicalchannel (e.g., PUSCH) carrying uplink data. According to theself-contained subframe structure, DL transmission and UL transmissionmay be sequentially performed in one subframe, and thustransmission/reception of DL data and reception/transmission of ULACK/NACK for the DL data may be performed in one subframe. As a result,the time taken to retransmit data when a data transmission error occursmay be reduced, thereby minimizing the latency of final datatransmission.

In such a self-contained subframe structure, a time gap is needed forthe process of switching from the transmission mode to the receptionmode or from the reception mode to the transmission mode of the eNB andUE. On behalf of the process of switching between the transmission modeand the reception mode, some OFDM symbols at the time of switching fromDL to UL in the self-contained subframe structure are set as a guardperiod (GP).

<Analog Beamforming>

In millimeter wave (mmW), the wavelength is shortened, and thus aplurality of antenna elements may be installed in the same area. Forexample, a total of 100 antenna elements may be installed in a 5-by-5 cmpanel in a 30 GHz band with a wavelength of about 1 cm in a2-dimensional array at intervals of 0.5λ (wavelength). Therefore, inmmW, increasing the coverage or the throughput by increasing thebeamforming (BF) gain using multiple antenna elements is taken intoconsideration.

If a transceiver unit (TXRU) is provided for each antenna element toenable adjustment of transmit power and phase, independent beamformingis possible for each frequency resource. However, installing TXRU in allof the about 100 antenna elements is less feasible in terms of cost.Therefore, a method of mapping a plurality of antenna elements to oneTXRU and adjusting the direction of a beam using an analog phase shifteris considered. This analog beamforming method may only make one beamdirection in the whole band, and thus may not perform frequencyselective beamforming (BF), which is disadvantageous.

Hybrid BF with B TXRUs that are fewer than Q antenna elements as anintermediate form of digital BF and analog BF may be considered. In thecase of hybrid BF, the number of directions in which beams may betransmitted at the same time is limited to B or less, which depends onthe method of collection of B TXRUs and Q antenna elements.

Unlike the conventional LTE/LTE-A system where all UEs and eNBs performsignal transmission and reception on a 1 ms basis due to the TTI with afixed length of 1 ms, the present invention proposes the system where aUE and an eNB can transmit and receive signals using a plurality of TTIlengths in the state that the TTI has a plurality of lengths. Inparticular, the present invention proposes a method for allowing an eNBand a UE to communicate to each other by supporting various TTI lengthsand variability thereof in the state that the TTI length can be changedand a multiplexing scheme for each channel and UE. Although the presentinvention is described based on the conventional LTE/LTE-A system, theinvention can be applied to other systems including the LTE/LTE-A systemor the RAT.

The sPDCCH referred to in the present invention may include a PDCCHtransmitted in the new RAT environment as well as a PDCCH transmitted inan sTTI in the LTE/LTE-A system.

To transmit data using a TTI of which the length is dynamically changedbased on a plurality of TTI lengths, a control channel (e.g., sPDCCH)for scheduling the data should also be transmitted using varioustransmission time lengths. For example, to schedule data transmittedwith a short TTI length, the sPDCCH also needs to be transmitted with ashort transmission time length. On the contrary, to schedule datatransmitted with a long TTI length, the sPDCCH may also be transmittedwith a long transmission time length. Thus, an SPDCCH search space needsto be designed such that the transmission time length of the sPDCCH canbe dynamically changed depending on the size of the TTI, where data istransmitted.

FIG. 11 illustrates an sPDCCH and transmission of a corresponding sPDSCHin a subframe where a legacy PDCCH is present.

Considering eNB's sPDCCH transmission flexibility, it may be helpful totransmit the sPDCCH using various lengths. For example, when the sPDSCHis transmitted in a partial OFDM symbol(s) in a specific PRB, if thesPDCCH is able to be transmitted in the remaining OFDM symbol(s) in thespecific PRB, it is possible to achieve efficient use of resources.

The present invention proposes an sPDCCH search space where the sPDCCHcan have various transmission lengths and the SPDCCH transmission timelength (hereinafter abbreviated as the transmission length) can bedynamically selected and then transmitted.

As described above, the legacy PDCCH is transmitted on an aggregation ofone or more CCEs, each including 9 REGs. The 9 REGs in each CCE aredistributed through interleaving in the time and frequency domains. Thatis, the legacy PDCCH spans an OFDM symbol(s) included in the legacycontrol region in the time domain and is distributed over the systembandwidth in the frequency domain. In the case of the legacy PDCCH, aPDCCH monitoring window is configured with an OFDM symbol(s) indicatedby the PCFICH in each downlink time interval except the discontinuousreception (DRX) duration. On the other hand, the EPDCCH is configuredwith an aggregation of one or more ECCEs. If the EPDCCH is configured tobe transmitted through distribution, each ECCE of the EPDCCH isconfigured with EREGs from a plurality of PRB pairs. If the EPDCCH isconfigured to be transmitted through localization, it is configured withEREGs from a single PRB pair. Since EREGs are configured with REsdistributed in a single PRB pair, the EPDCCH is transmitted across fromthe start OFDM symbol of the EPDCCH in a subframe and the last OFDMsymbol of the subframe in the corresponding PRB pair. Eventually, in thecase of the EPDCCH, an EPDCCH monitoring window is configured with froman OFDM symbol set to the EPDCCH start OFDM symbol to the last OFDMsymbol in the subframe where the EPDCCH is configured.

To allow the eNB to transmit the sPDCCH by dynamically selecting thetransmission length, a method for informing a UE(s) of the PDCCHmonitoring window through the PCFICH like the legacy PDCCH can beconsidered. However, if the PCFICH is transmitted in new RAT environmentoperating based on analog beamforming (ABF), the ABF is applied toPCFICH transmission so that only UEs along the corresponding beamdirection can know the number of OFDM symbols used for PDCCHtransmission. For example, assuming that the PCFICH is transmitted inthe first OFDM symbol, if a different beam direction is configured foreach DL control channel symbol, UEs corresponding to targets where a DLcontrol channel is transmitted in the second OFDM symbol may not detectthe PCFICH transmitted in the first OFDM symbol. However, if the PCFICHis transmitted in each OFDM symbol where the PDCCH can be transmitted,downlink control overhead may be significantly increased due to theincreased PCFICH transmission.

Therefore, according to the present invention, the UE can be configuredto perform monitoring of a plurality of sPDCCH transmission lengths T inone sPDCCH search space in order to enable the eNB to transmit thesPDCCH by dynamically selecting the transmission length. In the sPDCCHsearch space, the UE can monitor sPDCCH decoding candidates (i.e.,sPDCCH candidates) having multiple T values and sPDCCH decodingcandidates having multiple ECCE aggregation levels in the frequencydomain. That is, when resources for transmitting the sPDCCH span T OFDMsymbol(s) in the time domain and are configured with L ECCE(s) in thefrequency domain, the UE can monitor sPDCCH decoding candidates forvarious combinations of {L, T} in the SPDCCH search space.

<A. sPDCCH Search Space>

FIG. 12 illustrates an sPDCCH search space according to the presentinvention.

An sPDCCH monitoring window corresponding to a time unit where the UEperform monitoring for the sPDCCH (i.e., the time length of the sPDCCHsearch space) can be composed of multiple OFDM symbols. Specifically,the sPDCCH monitoring window can be configured as follows.

-   -   Option (a): The length of the sPDCCH monitoring window may be        fixed to one subframe. For example, referring to FIG. 12 (a),        when the legacy PDCCH resource region is not included in the        sPDCCH monitoring window, the length of the sPDCCH monitoring        window may be twelve OFDM symbols at all times.    -   Option (b): The length of the sPDCCH monitoring window may be        equal to the maximum TTI length among TTI lengths supported by        the cell. Alternatively, the length of the sPDCCH monitoring        window may be equal to the maximum TTI length among TTI        length(s) monitored by the UE. When the maximum TTI length        corresponds to one subframe or twelve OFDM symbols except the        legacy PDCCH region, Option (b) becomes identical to Option (a).        The maximum TTI length may be greater than 1 ms. If the maximum        TTI length monitored by the UE is four subframes, the length of        the sPDCCH monitoring window also becomes four subframes. FIG.        12 (b) illustrates sPDCCH monitoring windows when the maximum        TTI length monitored by the UE is four OFDM symbols.    -   Option (c): The length of the sPDCCH monitoring window may be        differently defined according to the time length in which the        sPDCCH is transmitted. For example, the monitoring window for        the sPDCCH of which the transmission length is T OFDM symbol(s)        may be T OFDM symbol(s). If the UE intends to monitor the sPDCCH        with respect to multiple sPDCCH transmission lengths, the UE may        monitor the sPDCCH using a different sPDCCH monitoring window        for each of the multiple sPDCCH transmission lengths T.

Frequency resources where the UE performs monitoring for the sPDCCH maybe configured with a partial PRB(s). A PRB(s) region constituting thesPDCCH search space may be configured as follows.

-   -   Option (1): The PRB(s) region where the UE performs monitoring        for the SPDCCH may be the same with respect to all sPDCCH        transmission lengths. The PRB(s) region where the UE performs        monitoring for the sPDCCH may be fixed or informed the UE        through a higher layer signal.    -   Option (2): The PRB(s) region where the UE performs monitoring        for the SPDCCH may vary in all sPDCCH transmission lengths. That        is, the number and/or location of PRB(s) to be monitored by the        UE with respect to the individual sPDCCH transmission lengths T        may be given separately. The PRB region for monitoring the        sPDCCH with respect to each sPDCCH transmission length may be        fixed or informed the UE through a higher layer signal.

<B. Resources of sPDCCH Candidates>

FIG. 13 illustrates sPDCCH candidates according to the presentinvention.

As illustrated in FIG. 13, one sPDCCH includes L (consecutive ornon-consecutive) ECCE(s) existing in an sPDCCH monitoring PRB(s) in thefrequency domain and T consecutive OFDM symbol(s) existing in the sPDCCHmonitoring window in the time domain. The number L of ECCEs for thesPDCCH transmission and the number T of OFDM symbols for the sPDCCHtransmission may have a plurality of values, respectively. For example,the number L of ECCEs where the sPDCCH can be transmitted may be {1, 2,4, 8}, and the number T of OFDM symbols in which the sPDCCH can betransmitted may be {2, 4, 12}.

Time Resources of sPDCCH Candidates

FIG. 14 illustrates a time resource(s) of sPDCCH candidates according tothe present invention.

When the sPDCCH is transmitted in T OFDM symbol(s), the sPDCCHtransmission may start at a plurality of OFDM symbols within the sPDCCHmonitoring window. For example, as illustrated in FIG. 14, in the caseof the sPDCCH with the sPDCCH transmission length T, the transmissionthereof may start with a period of T OFDM symbol(s) in the sPDCCHmonitoring window. The UE performs monitoring of the sPDCCH with respectto the sPDCCH transmission length T every T OFDM symbol(s) within thesPDCCH monitoring window.

ECCE Resources of sPDCCH Candidates

The present invention proposes an ECCE resource mapping method suitablewhen a plurality of sPDCCH transmission lengths T are supported in thesPDCCH search space. In the prior art, CCE resource mapping for thelegacy PDCCH has been performed in an OFDM symbol(s) region where thePDCCH was transmitted, and ECCE resource mapping for the EPDCCH has beenperformed on a subframe basis. That is, in the case of the legacy(E)PDCCH, the (E)PDCCH has been monitored using a single transmissiontime length. On the other hand, in the case of the sPDCCH with theplurality of transmission lengths T, an (E)CCE resource mapping methodtherefor needs to be defined. The present invention proposes thefollowing ECCE resource mapping methods for the sPDCCH.

ECCE Resource Mapping Method 1

To support the plurality of sPDCCH transmission lengths T in the sPDCCHsearch space, the legacy ECCE resource mapping may be reused. One EREGis configured using 9 REs existing in one PRB, and one ECCE isconfigured using 4 EREGs among EREGs existing in an EPDCCH-PRB set.

The legacy ECCE resource mapping is performed based on one subframe. Inthe case of the sPDCCH transmitted using only T OFDM symbol(s) in asubframe, the SPDCCH transmission may be rate-matched (or punctured) inOFDM symbol(s) except the T OFDM symbol(s) where the sPDCCH istransmitted.

Even though the sPDCCH is transmitted using the same aggregation level(AL), the actual amount of resources used for the sPDCCH transmissionmay vary depending on the value (size) of the transmission length T usedfor the sPDCCH transmission. For example, in the case of the sPDCCH withT=12 OFDM symbols, the amount of resources used for the sPDCCHtransmission is about three times greater than that used fortransmitting the sPDCCH with T=4 OFDM symbols although the same AL isused. Therefore, to support the same range of effective code rates (oreffective sPDCCH transmission resources) in transmitting the sPDCCH, thepresent invention proposes to change the range (or values) of the AL forthe sPDCCH transmission according to the value of T. For example,assuming that the maximum value of T supported by the cell or monitoredby the UE is Tmax and ALs that can be held by the sPDCCH transmittedwith Tmax are {AL1, AL2, AL3, AL4}, ALs that can be held by the sPDCCHtransmitted with T=Tmax/D may be set to {AL1*D, AL2*D, AL3*D, AL4*D},where D indicates a ratio of Tmax to T (i.e., D=Tmax/T).

ECCE Resource Mapping Method 2

FIG. 15 illustrates an ECCE resource mapping method according to thepresent invention.

In order to support the plurality of sPDCCH transmission lengths T inthe sPDCCH search space, EREG to RE mapping may be performed based onthe maximum number T (Tmax) of OFDM symbols supported by the cell ormonitored by the UE. In addition to this, ECCE to EREG mapping may beperformed using EREGs existing in the same number Tmax of OFDM symbols.Alternatively, the EREG to RE mapping and ECCE to EREG mapping may beperformed based on OFDM symbols included in the sPDCCH monitoringwindow. In the case, the value of Tmax may be equal to the sPDCCHmonitoring window. For example, if the values of T for the sPDCCH are{1, 2, 4}, the EREG to RE mapping may be performed based on four OFDMsymbols corresponding to the Tmax value.

As described above, ECCE resource mapping for the sPDCCH can beperformed based on the Tmax OFDM symbol(s) or sPDCCH monitoring window.When the SPDCCH is transmitted only in T OFDM symbol(s) among the TmaxOFDM symbol(s) or in the sPDCCH monitoring window, the SPDCCHtransmission may be rate-matched (or punctured) in an OFDM symbol(s)region except the T OFDM symbol(s) region where the SPDCCH istransmitted. For example, as shown in FIG. 15, when the sPDCCHmonitoring window is composed of four OFDM symbols, the ECCE resourcemapping is performed in each sPDCCH monitoring window. Since sPDCCH1 hasT=2 and is transmitted using only the first and second OFDM symbols inthe sPDCCH monitoring window thereof, the sPDCCH transmission may berate-matched (or punctured) in a region consisting of the third andfourth OFDM symbols in the corresponding sPDCCH monitoring window.Similarly, since sPDCCH2 has T=2 and is transmitted using only the thirdand fourth OFDM symbols in the sPDCCH monitoring window thereof, thesPDCCH transmission may be rate-matched (or punctured) in a regionconsisting of the first and second OFDM symbols in the correspondingsPDCCH monitoring window. Further, since sPDCCH3 has T=1 and istransmitted using only the second OFDM symbol in the sPDCCH monitoringwindow thereof, the sPDCCH transmission may be rate-matched (orpunctured) in a region consisting of the first, third and fourth OFDMsymbols in the corresponding sPDCCH monitoring window.

Although the sPDCCH transmission is performed using the same AL, theactual amount of resources used for the sPDCCH transmission variesaccording to the value (size) of T used for the sPDCCH transmission. Forexample, in the case of the sPDCCH with T=4 OFDM symbols, the amount ofresources used for the sPDCCH transmission is about two times greaterthan that used for transmitting the sPDCCH with T=2 OFDM symbolsalthough the same AL is used. Therefore, to achieve the same range ofeffective code rates (or effective sPDCCH transmission resources) intransmitting the sPDCCH, the present invention proposes to change therange (or values) of the AL for the sPDCCH transmission according to thevalue of T. For example, assuming that the maximum value of T supportedby the cell or monitored by the UE is Tmax and ALs that can be held bythe sPDCCH transmitted with Tmax are {AL1, AL2, AL3, AL4}, ALs that canbe held by the sPDCCH transmitted with T=Tmax/D may be set to {AL1*D,AL2*D, AL3*D, AL4*D}.

ECCE Resource Mapping Method 3

FIG. 16 illustrates another ECCE resource mapping method according tothe present invention.

In order to support the plurality of sPDCCH transmission lengths T inthe sPDCCH search space, the EREG to RE mapping may be performed basedon the minimum number T (hereinafter referred to as Tmin) of OFDMsymbols supported by the cell or monitored by the UE.

In addition to this, the ECCE to EREG mapping may be performed usingEREGs existing in the same number Tmin of OFDM symbols. For example,when the values of T for the sPDCCH transmission are {2, 4, 12}, theEREG to RE mapping may be performed based on two OFDM symbolscorresponding to the Tmin value. To support the plurality of sPDCCHtransmission lengths T in the sPDCCH search space, the EREG to REmapping and ECCE to EREG mapping may be performed based on a single OFDMsymbol. That is, one ECCE may be composed of REs existing in the TminOFDM symbols or one OFDM symbol.

When the ECCE is composed of REs in one OFDM symbol, the sPDCCH with theAL value of L may be transmitted in T OFDM symbol(s) using L ECCEs ineach OFDM symbol. The total number of ECCE resources used for the sPDCCHtransmission is L*T. When the ECCE is composed of REs in two OFDMsymbols, the sPDCCH is transmitted in the T OFDM symbol(s) using L ECCEsevery two OFDM symbols, and the total number of ECCE resources used forthe sPDCCH transmission is L*T/2.

Although the sPDCCH transmission is performed using the same AL, theactual amount of resources used for the sPDCCH transmission variesaccording to the value (size) of T used for the sPDCCH transmission. Forexample, in the case of the sPDCCH with T=4 OFDM symbols, the amount ofresources used for the sPDCCH transmission is about two times greaterthan that used for transmitting the sPDCCH with T=2 OFDM symbolsalthough the same AL is used. Therefore, to achieve the same range ofeffective code rates (or effective sPDCCH transmission resources) intransmitting the sPDCCH, the present invention proposes to change therange (or values) of the AL for the sPDCCH transmission according to thevalue of T. For example, assuming that the minimum value of T supportedby the cell or monitored by the UE is Tmin and ALs that can be held bythe sPDCCH transmitted with Tmin are {AL1, AL2, AL3, AL4}, ALs that canbe held by the sPDCCH transmitted with T=Tmax/D may be set to {AL1/D,AL2/D, AL3/D, AL4/D}.

ECCE Resource Mapping Method 4

FIG. 17 illustrates still another ECCE resource mapping method accordingto the present invention.

In order to support the plurality of sPDCCH transmission lengths T inthe sPDCCH search space, the EREG to RE mapping may be performed basedon the minimum number T (Tmin) of OFDM symbols supported by the cell ormonitored by the UE. That is, one EREG may be composed of a plurality ofREs existing the Tmin OFDM symbols.

For example, when the values of T for the sPDCCH transmission are {2, 4,12}, the EREG to RE mapping may be performed in an OFDM symbol groupconsisting of two OFDM symbols corresponding to the Tmin value.

One ECCE may be defined using EREGs existing in several OFDM symbolgroups. For example, when the sPDCCH monitoring window includes twelveOFDM symbols and it is divided into a total of six OFDM symbol groups,each of which consisting of two consecutive OFDM symbols, the EREG to REmapping may be performed in one OFDM symbol group. On the other hand, inthe case of the sPDCCH with the transmission length T, the ECCE to EREGmapping may be performed in T/2 OFDM symbol groups where T OFDM symbolsfor the sPDCCH transmission are present. That is, one ECCE is configuredwith a plurality of EREGs existing in the T/2 OFDM symbol groups wherethe sPDCCH is transmitted.

For example, as illustrated in FIG. 17, the sPDCCH monitoring window maybe composed of twelve OFDM symbols, and one EREG is configured withresources in two consecutive OFDM symbols. In the case of the sPDCCHwith the transmission length T=4 shown in FIG. 17 (a), one ECCE isconfigured using EREGs existing in a region consisting of four OFDMsymbols in which the sPDCCH is transmitted. When one ECCE is composed offour EREGs, the one ECCE may include four EREGs among EREGs existing inthe region configured with T=4 OFDM symbols where the sPDCCH istransmitted. The sPDCCH with L=4, which is transmitted in T=4 OFDMsymbols, is transmitted via L=4 ECCEs, which are configured using theEREGs existing in the corresponding region configured with T=4 OFDMsymbols. In the case of T=12, one ECCE is configured using EREGs exitingin a region consisting of twelve OFDM symbols where the sPDCCH istransmitted as shown in FIG. 17 (b). When one ECCE is composed of fourEREGs, the one ECCE may include four EREGs among EREGs existing in theregion configured with T=12 OFDM symbols where the sPDCCH istransmitted. The sPDCCH with L=4, which is transmitted in T=12 OFDMsymbols, is transmitted via L=4 ECCEs, which are configured using theEREGs existing in the corresponding region configured with T=12 OFDMsymbols.

Therefore, when this ECCE resource mapping method is used, the EREG toRE mapping is the same regardless of the value of T for the sPDCCHtransmission, whereas the ECCE to EREG mapping varies according to thevalue of T for the sPDCCH transmission.

If the sPDCCH is transmitted on the same AL, the same amount ofresources is used for the sPDCCH transmission although the value (size)of T used for the sPDCCH transmission is changed. Therefore, the AL usedfor the sPDCCH transmission can have the same range (or values) withrespect to all values of T.

ECCE Resource Mapping Method 5

FIG. 18 illustrates a further ECCE resource mapping method according tothe present invention.

In order to support the plurality of sPDCCH transmission lengths T inthe sPDCCH search space, the EREG to RE mapping and ECCE to EREG mappingmay be performed based on the number (=T) of OFDM symbols where thesPDCCH is transmitted.

The EREG to RE mapping may be performed in the T OFDM symbols where thesPDCCH is transmitted. That is, in the case of the sPDCCH with thetransmission length T, one EREG may be composed of a plurality of REs inthe T OFDM symbols.

In addition, one ECCE may be defined using a plurality of EREGs existingin the T OFDM symbols where the sPDCCH is transmitted.

For example, as shown in FIG. 18 (a), in the case of the sPDCCH with thetransmission length T=4, one EREG is configured using a plurality of REsamong REs existing in a region configured with four OFDM symbols wherethe sPDCCH is transmitted. In addition, one ECCE is configured using aplurality of EREGs existing in the region configured with the four OFDMsymbols used for the sPDCCH transmission. When one ECCE is composed offour EREGs, the one ECCE may include four EREGs among EREGs existing inthe region configured with T=4 OFDM symbols where the sPDCCH istransmitted. The sPDCCH with L=4, which is transmitted in T=4 OFDMsymbols, is transmitted via L=4 ECCEs, which are configured using theEREGs existing in the corresponding region configured with T=4 OFDMsymbols. In the case of the sPDCCH with T=12, one EREG is configuredusing a plurality of REs among RES existing in a region composed oftwelve OFDM symbols where the sPDCCH is transmitted, and one ECCE isconfigured using a plurality of EREGs exiting in the region consistingof twelve OFDM symbols where the sPDCCH is transmitted as shown in FIG.18 (b). When one ECCE is composed of four EREGs, the one ECCE mayinclude four EREGs among EREGs existing in the region configured withT=12 OFDM symbols where the sPDCCH is transmitted. The sPDCCH with L=4,which is transmitted in T=12 OFDM symbols, is transmitted via L=4 ECCEs,which are configured using the EREGs existing in the correspondingregion configured with T=12 OFDM symbols.

When this ECCE resource mapping method is used, the EREG to RE mappingand ECCE to EREG mapping may vary according to the value of T for thesPDCCH transmission.

If the sPDCCH is transmitted on the same AL, the same amount ofresources is used for the sPDCCH transmission although the value (size)of T used for the sPDCCH transmission is changed. Therefore, the AL usedfor the sPDCCH transmission (or values) with respect to all T values.

FIG. 19 is a block diagram illustrating elements of a transmittingdevice 10 and a receiving device 20 for implementing the presentinvention.

The transmitting device 10 and the receiving device 20 respectivelyinclude Radio Frequency (RF) units 13 and 23 capable of transmitting andreceiving radio signals carrying information, data, signals, and/ormessages, memories 12 and 22 for storing information related tocommunication in a wireless communication system, and processors 11 and21 operationally connected to elements such as the RF units 13 and 23and the memories 12 and 22 to control the elements and configured tocontrol the memories 12 and 22 and/or the RF units 13 and 23 so that acorresponding device may perform at least one of the above-describedembodiments of the present invention.

The memories 12 and 22 may store programs for processing and controllingthe processors 11 and 21 and may temporarily store input/outputinformation. The memories 12 and 22 may be used as buffers.

The processors 11 and 21 generally control the overall operation ofvarious modules in the transmitting device and the receiving device.Especially, the processors 11 and 21 may perform various controlfunctions to implement the present invention. The processors 11 and 21may be referred to as controllers, microcontrollers, microprocessors, ormicrocomputers. The processors 11 and 21 may be implemented by hardware,firmware, software, or a combination thereof. In a hardwareconfiguration, application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), or field programmable gate arrays(FPGAs) may be included in the processors 11 and 21. Meanwhile, if thepresent invention is implemented using firmware or software, thefirmware or software may be configured to include modules, procedures,functions, etc. performing the functions or operations of the presentinvention. Firmware or software configured to perform the presentinvention may be included in the processors 11 and 21 or stored in thememories 12 and 22 so as to be driven by the processors 11 and 21.

The processor 11 of the transmitting device 10 performs predeterminedcoding and modulation for a signal and/or data scheduled to betransmitted to the outside by the processor 11 or a scheduler connectedwith the processor 11, and then transfers the coded and modulated datato the RF unit 13. For example, the processor 11 converts a data streamto be transmitted into K layers through demultiplexing, channel coding,scrambling, and modulation. The coded data stream is also referred to asa codeword and is equivalent to a transport block which is a data blockprovided by a MAC layer. One transport block (TB) is coded into onecodeword and each codeword is transmitted to the receiving device in theform of one or more layers. For frequency up-conversion, the RF unit 13may include an oscillator. The RF unit 13 may include N_(t) (where N_(t)is a positive integer) transmit antennas.

A signal processing process of the receiving device 20 is the reverse ofthe signal processing process of the transmitting device 10. Undercontrol of the processor 21, the RF unit 23 of the receiving device 20receives radio signals transmitted by the transmitting device 10. The RFunit 23 may include N_(r) (where N_(r) is a positive integer) receiveantennas and frequency down-converts each signal received throughreceive antennas into a baseband signal. The processor 21 decodes anddemodulates the radio signals received through the receive antennas andrestores data that the transmitting device 10 intended to transmit.

The RF units 13 and 23 include one or more antennas. An antenna performsa function for transmitting signals processed by the RF units 13 and 23to the exterior or receiving radio signals from the exterior to transferthe radio signals to the RF units 13 and 23. The antenna may also becalled an antenna port. Each antenna may correspond to one physicalantenna or may be configured by a combination of more than one physicalantenna element. The signal transmitted from each antenna cannot befurther deconstructed by the receiving device 20. An RS transmittedthrough a corresponding antenna defines an antenna from the view pointof the receiving device 20 and enables the receiving device 20 to derivechannel estimation for the antenna, irrespective of whether the channelrepresents a single radio channel from one physical antenna or acomposite channel from a plurality of physical antenna elementsincluding the antenna. That is, an antenna is defined such that achannel carrying a symbol of the antenna can be obtained from a channelcarrying another symbol of the same antenna. An RF unit supporting aMIMO function of transmitting and receiving data using a plurality ofantennas may be connected to two or more antennas.

In the embodiments of the present invention, a UE operates as thetransmitting device 10 in UL and as the receiving device 20 in DL. Inthe embodiments of the present invention, an eNB operates as thereceiving device 20 in UL and as the transmitting device 10 in DL.Hereinafter, a processor, an RF unit, and a memory included in the UEwill be referred to as a UE processor, a UE RF unit, and a UE memory,respectively, and a processor, an RF unit, and a memory included in theeNB will be referred to as an eNB processor, an eNB RF unit, and an eNBmemory, respectively.

According to the present invention, the eNB processor may control theeNB RF unit to transmit a PDCCH in a random number of OFDM symbolswithin the maximum time length Tmax capable of transmitting the PDCCHwithout informing the number of OFDM symbols occupied by the PDCCH.

Specifically, the eNB processor may control the eNB RF unit to transmitthe PDCCH in a search space configured according to any one of themethods proposed in section A. The UE processor may control the eNB RFunit to receive the PDCCH in the search space configured according toany one of the methods proposed in section A. In addition, the UEprocessor may be configured to monitor decoding candidates over a randomnumber of OFDM symbols and decode the PDCCH among the decodingcandidates.

Each of the eNB processor and UE processor may be configured to map anEREG to REs and/or map an ECCE to EREGs according to any one of themethods proposed in section A.

The eNB processor may adjust the number of ECCEs based on the number ofthe OFDM symbols occupied by the PDCCH according to any one of theproposals of the present invention. The UE processor may monitor eachdecoding candidate according to any one of the proposals of the presentinvention by assuming that the number of occupied ECCEs varies accordingto the number of the OFDM symbols occupied by the PDCCH.

As described above, the detailed description of the preferredembodiments of the present invention has been given to enable thoseskilled in the art to implement and practice the invention. Although theinvention has been described with reference to exemplary embodiments,those skilled in the art will appreciate that various modifications andvariations can be made in the present invention without departing fromthe spirit or scope of the invention described in the appended claims.Accordingly, the invention should not be limited to the specificembodiments described herein, but should be accorded the broadest scopeconsistent with the principles and novel features disclosed herein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to an eNB, a UE,or other devices in a wireless communication system.

The invention claimed is:
 1. A method for receiving a downlink channelby a user equipment (UE) in a wireless communication system, the methodcomprising: receiving a downlink control channel carrying downlinkcontrol information within a transmission time interval (TTI); andreceiving a downlink data channel based on the downlink controlinformation, wherein receiving of the downlink control channel comprisesmonitoring a first downlink control channel candidate spanning T1orthogonal frequency division multiplexing (OFDM) symbols within the TTIand monitoring a second downlink control channel candidate spanning T2OFDM symbols within the TTI, wherein the downlink control channelcomprises the first downlink control channel candidate or the seconddownlink control channel candidate, and wherein T1 is different from T2.2. The method according to claim 1, wherein the TTI is equal to orsmaller than 0.5 ms in a time domain.
 3. The method according to claim1, wherein the TTI is configured within a different TTI with a length of1 ms in a time domain.
 4. The method according to claim 1, wherein thefirst downlink control channel candidate occupies L1 control channelelements (CCEs), wherein the second downlink control channel candidateoccupies L2 CCEs, and wherein L2=(T1/T2)*L1, where L1 and L2 arepositive integers.
 5. A method for transmitting a downlink channel by abase station (BS) in a wireless communication system, the methodcomprising: transmitting a downlink control channel carrying downlinkcontrol information within a transmission time interval (TTI); andtransmitting a downlink data channel based on the downlink controlinformation within the TTI, wherein transmitting the downlink controlchannel comprises transmitting the downlink control information througha first downlink control channel candidate spanning T1 orthogonalfrequency division multiplexing (OFDM) symbols within the TTI or througha second downlink control channel candidate spanning T2 OFDM symbolswithin the TTI, and wherein T1 is different from T2.
 6. The methodaccording to claim 5, wherein the TTI is equal to or smaller than 0.5 msin a time domain.
 7. The method according to claim 5, wherein the TTI isconfigured within a different TTI with a length of 1 ms in a timedomain.
 8. The method according to claim 5, wherein the first downlinkcontrol channel candidate occupies L1 control channel elements (CCEs),wherein the second downlink control channel candidate occupies L2 CCEs,and wherein L2=(T1/T2)*L1, where L1 and L2 are positive integers.
 9. Auser equipment (UE) for receiving a downlink channel in a wirelesscommunication system, the UE comprising: a transceiver; at least oneprocessor; and at least one computer memory operably connectable to theat least one processor and storing instructions that, when executed bythe at least one processor, perform operations comprising: receiving,via the transceiver, a downlink control channel carrying downlinkcontrol information within a transmission time interval (TTI); andreceiving, via the transceiver, a downlink data channel based on thedownlink control information within the TTI, wherein the receiving thedownlink control channel comprises monitoring a first downlink controlchannel candidate spanning T1 orthogonal frequency division multiplexing(OFDM) symbols within the TTI and monitoring a second downlink controlchannel candidate spanning T2 OFDM symbols within the TTI, wherein thedownlink control channel comprises the first downlink control channelcandidate or the second downlink control channel candidate, and whereinT1 is different from T2.
 10. The UE according to claim 9, wherein theTTI is equal to or smaller than 0.5 ms in a time domain.
 11. The UEaccording to claim 9, wherein the TTI is configured within a differentTTI with a length of 1 ms in a time domain.
 12. The UE according toclaim 9, wherein the first downlink control channel candidate occupiesL1 control channel elements (CCEs), wherein the second downlink controlchannel candidate occupies L2 CCEs, and wherein L2=(T1/T2)*L1, where L1and L2 are positive integers.
 13. A base station (BS) for transmitting adownlink channel in a wireless communication system, the BS comprising:a transceiver; at least one processor; and at least one computer memoryoperably connectable to the at least one processor and storinginstructions that, when executed by the at least one processor, performoperations comprising: transmitting, via the transceiver, a downlinkcontrol channel carrying downlink control information within atransmission time interval (TTI); and transmitting, via the transceiver,a downlink data channel based on the downlink control information,wherein the transmitting the downlink control channel comprisestransmitting the downlink control information through a first downlinkcontrol channel candidate spanning T1 orthogonal frequency divisionmultiplexing (OFDM) symbols within the TTI or through a second downlinkcontrol channel candidate spanning T2 OFDM symbols within the TTI, andwherein T1 is different from T2.
 14. The BS according to claim 13,wherein the TTI is equal to or smaller than 0.5 ms in a time domain. 15.The BS according to claim 13, wherein the TTI is configured within adifferent TTI with a length of 1 ms in a time domain.
 16. The BSaccording to claim 13, wherein the first downlink control channelcandidate occupies L1 control channel elements (CCEs), wherein thesecond downlink control channel candidate occupies L2 CCEs, and whereinL2=(T1/T2)*L1, where L1 and L2 are positive integers.